Hi if you currently using 17" definitely is not comfort to compare with 16" rims and tyre more sidewall.

If 17" I would recommend you on Goodyear Eagle F1 Asym 2.

Low noise and more stopping power.
Made in Germany some more.

For comfort, surely better change to 16'. You can use 205/55/R16, it will have much thicker sidewall hence gives you a lot more comfort and safety from potholes. But you'll loose just a little bit of performance due to 1 cm narrower tire, and the thicker tire will be less responsive. So it's your choice, prefer more comfort or maintain the performance with stiffer ride quality. I suggest if you're fine with the current comfort level, then just stay with the current size. If you cannot stand it anymore, then change to 16'.

As for the brands, it's up to your budget, tire size, and what performance level you're looking for. 16' will have more choices on the lower-middle performance ranges while 17' will have more on the middle-high performance ranges. Pirelli, Michelin, BS, Continental, Yokohama, Toyo, GY, Dunlop, GT Radial, Federal, Hankook, they all trusted good brands. Some like GT Radial are cheaper, some like Michelin & Pirelli are rather expensive.

205/50 will be about 0.5cm thicker sidewall than the 215/45, hence it will be a bit more comfortable with just a slight reduction in grip due to 1cm narrower tire, but since you don't drive fast, it should be ok. You can compensate that by getting a more high performance/grip tire and you would not suffer drop in grip. For example if now you're using tire with UTQG rating of tread wear 400, traction A, temp A, then can upgrade to one with tread wear 300, traction AA, temp. A. With this, even though you use 1cm narrower tire, the performance would actually still be better.

stick to stock size, no need alteration as you're already on 17"
215/45/17 easier to find sizes and cheaper too as more tires produced for popular sizes hence cheaper price too.

for your criteria, since no budget is specified, consider yokohama Advan DB, it is their flagship comfort/low NVH tire
or can consider Nitto Invo, also their flagship in luxury/comfort/low NVH tires
if wet grip is your priority while you don't mind a little bit nvh compromise (compared to advan db/invo anyways) you can go with good year's flagship tire - Eagle F1 asymmetric 2

if you want safety (as you said, better wet grip) and good NVH, such tires will have to sacrifice on durability/lasting tread as they are typically constructed much softer
however if you don't drive fast/aggressive, they WILL last easily AT LEAST 50-60k km as these tires afaik are rated OVER 300 treadwear assuming you properly maintain them with correct pressure, proper alignment etc

The UTQG rating is actually stated at the sidewall of the tires, usually at the outer edge near the tread pattern. Some brands (but not all) also mention them in their product listing in their websites, so it's easy to check.

For 1st question, again like I said above, if you feel 215/45 is still comfortable enough for you then ok to just remain using that size. If you want a bit more comfort then change to 205/50. The other 2 sizes (215/50 & 215/55) are too big already. If your rims is at least 7.5 inch wide than can also consider 225/45. This will give you slightly more comfort and also better grip since it's 1cm wider.

As for the 2nd question, there are so many types of tires out there for many different price range, so it's rather difficult to recommend specifically. I'm personally now using 17' GY F1-D5 which is very good performance but slightly noisy which is still acceptable/normal for high performance tires. Even better one should be the F1 Assymetric2, at a slightly more expensive price. Other good all-round high performance tire is the Michelin PS3, but further more expensive. Other tires which I considered myself last time were Yokohama Advan Sport & Toyo T1 Sport. If you want cheaper tires but still offers very good performance and reliable, can opt for GT Radial Champiro HPY which is on the same performance class as the above but at much cheaper price. Note that these are all ultra high performance (UHP) level tires with tread wear around low 300 or even lower which is just 1 or 2 level lower than semi-slick tires, hence the durability might not match those middle/lower level tires, but they offer very good grip.

most comfort should be Yokohama Advan DB, Nitto hard to say since it is just recently emerging in Malaysian market.

and yes, if you do not drive fast. eg: not over 100km/h in wet conditions, even basic cheap tires will suffice, however yes, having better tires will definitely be able to cope for emergency braking should it arises

for the 3 tires i mentioned, (for easy sake let's group comfort and nvh together):
1) goodyear
2) Yokohama
3) Nitto

however if you put wet grip as last, it'll be
1) Yokohama
2) Nitto
3) Goodyear
and depend if you want nitto's aggressive/unique tire tread styling (it is mainly marketed to american market, and it is under Toyo too btw ) and maybe slightly better performance, you can rate it above Yokohama's advan DB

For Michelin PS3, it is a jack of all trades, master of none tire.
it is quiet/comfortable, however won't be as comfortable/quiet as Nitto invo/Yokohama Advan DB. it performs good in wet conditions, however it won't ever be as good as GY Eagle F1 AS2 as that tire benchmarked by sports car under wet conditions and it is after all, GY's flagship tire while PS3 isn't michelin's flagship
That, and Michelin's tires are typically overpriced (of course one could probably argue the same with Yokohama's Advan lineup as it is their flagship tires) so personally i don't favor with Michelin tires at all

if anything, it's treadwear does last long, however i don't think it'll be any much longer than gy/nitto/yokohama.
treadwear wise its ps3 (320) > eagle f1 as2 (300) > nitto (260), can't seem to get utqg rating for yokohama, however it'll be around 300/300+ around ps3/goodyear
and long lasting treadwear tires *TYPICALLY* don't perform well in performance/comfort/nvh as they are harder tire compound

Yes, Michelin is pretty expensive, like Pirelli, Continental, & BS also.

Yokohama put their UTQG rating in their website, so it's easy to find out. The Advan Sport has tread wear only 180 or 240 depending on size.

not for Advan DB, although iinm their advan db does not have UTQG ratings as they tend to market advan sport over America since most oversea customers do demand performance in their luxury vehicles, not just comfort/nvh.

http://yokohamatire.jp/yrc/japan/searchbytirebrand.html
advan sport isn't exactly a comfort tire as you can see.
latest advan sport v105 (also uses their orange oil compound) are 240 treadwear rated

and oversea advan db isn't widely market which is why i don't think they have a proper UTQG rating.
That said, the old DB e-spec, has a 460 treadwear rating
http://www.tirerack.com/images/pdf/t_w_cat.pdf

For some sizes, the Advan Sport even have tread wear only 180, matching the Advan Neova.