If you're into classical piano, you might wanna consider a conventional upright piano rather than a digital piano, unless syou can find a cheap digital piano with features useful for your classical piano skills/techniques likes half-pedalling, key-touch sound sensitivitiy (not sure what's that called, it's not touch sensitivity... you only find these in high end digital piano). But then, if you don't mind these features and prefer the digital, then go ahead and try out each brand and models.

I suggest you to try out the different models than plainly listening to opinions. Each person will have their own views and brand suggestion. Use other's views and suggestions as a reference and then try it out yourself. The sound, touch and feeling from each brand and model is different.

Personally, I would suggest you to try out the latest Roland model with PHA-II keys, but it's not cheap for a Roland.
For closeness to the conventional piano, my personal view would be the Kawaii brand, to me, they have the closest "touch" feel of the conventional piano, with the sticky keys feeling.

If you want space and easy to move around, then I suggest you get a portable or sometimes known as STAGE Pianos (which some called Keyboard with Weighted Keys). Basically, keyboard/digital piano, they're the same thing, just different naming, a keyboard is simply a portable digital piano and they come in weighted keys or non-weighted keys. As technolgy advanced, they separate each into different categories, like Arrangers, Stage Pianos, Workstations, etc. It's simply keyboards with different features/functions, while keyboards are simply portable digital piano or vice versa, piano are keyboard instruments.

For Portable Digital Piano / Stage Piano, Roland's one will cost a bomb. You can try Yamaha one's, it's around 3K++ if I'm not wrong and it's quite good too.
Casio will come cheaper but I wouldn't really recommendeds it, why not spend extra little to get a better ones, you're going to use it for long time right?
Anyway, you should try out yourself whether these are good or not, it's just my personal opinions and suggestions.

Good Luck and All The Best!

S90 Stage Piano is using Balance Hammer Action. It's also not closed to a real piano. For Yamaha you'd have to go fo the GH technology.
What I like about the S90 (S90ES actually) is the sound. Really nice. But they keys are very plastic and if you jam on it, the sound of the keys are pretty audible. I can even hear it from a video recording, the demo of S90ES.

Then again, like I said before, different people have different feel and taste.

But there's one thing I believe everyone will experience:
If you've play on a high quality digital piano (or digital piano with good keys), and you go to another piano and play, the moment you touch it you will feel the difference.
I played on a Casio middle range and a high end, the feeling of the keys and hammer action is not good since I've playing on better one for me. So, it's best to test it out few models and decide. Opinions and feel can differ from different person.
Likewise, if you're an Acoustic Piano player, you'll find hard to get good digital piano with good keys and hammer action.

Hehe, that's why I did ask him/her to get a upright piano if can. I mentioned high quality is just as a comparison of keys and hammer action. And it doesn't necessarily be expensive ones for a good hammer action and keys (An example of Casio high end ones; even it was high end, the keys and hammer action are no match for some low end brands, based on my feel and opinions). Of course, those high end usually have more features which is more similar to a real Acoustic Piano or Grand Piano.

Even for low end, between different makes have different technology of implementing their keys and hammer action, and the feel and touch differs from one person to another. Most people would prefer the Yamaha, some Kawaii. But one should test out each to know which they prefer more, after all it's a BIG one time long term investment. You don't want to later played another competitor model and regrets you get the wrong one, right?

Sound would be another factor, and if both these clashes (e.g. Sound of Yamaha, touch of Kawaii), then it's the tough part to decide.

With your price, you could few choices already. Those low ends upright Digital would cost around 3K-5K depending on brand. But since your mentioned space, it'll be not much different from your current upright acoustic piano.
So, you should go for Portable ones or also known as Stage. You can check out Yamaha Portable Grand, it should cost around RM3000++ if I'm not wrong. Not sure if it comes with the stand or need to purchase separately tough.

I'm not so sure if Kawaii have one portable ones at that price,... since you have a Kawaii Acoustics, you'll most porbably prefer the Kawaii Digital as it resembles more to it and you're used to it.

Another choice not known by many is the Suzuki brand. Altought I have not really tested it, but I've seen the sales showing off the features of the piano, even for the low end version, it has an equalizer ability to adjust your tone (e.g. making the piano sound brighter/darker/mellow/etc...). Quite a nice feature but the sound quality still depends on the individual.

Maybe you can go and test out the few choices, it'll be easier to decide as you can be sure whether a digital can replace the feel and sound of the acoustic piano or acceptable. In anyway, both choice has it's 'hassle', buying a digital might not satisfy you (unless you can accept it and enjoy the features and making use of it),
not buying would save you money but you'll need to transport the acoustic piano and tune the piano from time to time.

Plus, you have to consider not disturbing your neighbour. A digital you can control the volume as well as use headphone when practicing or playing in the night. You can also bring it to your friends house to perform in party/etc (if you want). If you know how to use the feature, these digital piano is capable of simulating a band. You can see many videos in YouTube by people making use of these features.
A Good Example is here:
http://www.youtube.com/watch?v=-cvBGPfmRqM
This guy is using the Roland EXR-7s, an Interactive Arranger Keyboard.

But if you're into classical, then you might not really need those. Just a useful feature nice to have.