In that case you are using it like a wifi repeater

you will not get any of the benefits of mesh

Well, Mesh lets your device move from 1 unit to another unit without any interruption/disconnecting

and its smarter, so say like you have 3 units, they will talk to each other to send/receive the data, and if like one gets powered off the mesh will re-adjust

for best results I would say buy at least 2

one, to replace the router provided by tm/maxis/time, as the main "master" node
2nd, as your mesh node that will connect back to the main node wirelessly or wired (wired for better results)

if using wirelessly, getting "Tri-Band" mesh nodes are better as they have 2 radios, so they can talk to the other nodes while also talking to your devices
otherwise it has to take turns

mesh, specifically via 802.11 k / v / r allows for roaming between them, so your devices can easily move between them 2 without disconnecting

and different, because connecting deco to not deco main router, they dont/cant talk to each other about this roaming, the experience is not as good moving between them
so, you get wifi repeater like experience

and, more expensive deco mesh again, has the dual radio so you do not get the speed penalty because otherwise 1 radio has to talk to both your device and the upstream one, it can't do both at the same time so your speed suffers

I never recommend mixing setups, always stick to 1 setup, dont mix and match, modem -> deco directly

if you can pull wires, always do it
if cannot, then getting dual radio ones are best to prevent the speed decrease.

dont bother keeping whatever tm/maxis/time/etc give you, it's not good.

do you have a separate modem + router setup from tm or a single device from TM

if separate, keep the one without antennas, that's your modem, should be Huawei/FiberHome/ZTE/Nokia/Alcatel-Lucent branded
if 2 in 1, need to bridge mode it, ask main thread for guide

then, connect up your main mesh node with a ethernet cable to LAN1 of the modem
then, setup the Deco in PPPoE Mode, it will require a username and password, you can just ask TM for it, just tell them you want the PPPoE username and password
also select Unifi ISP when configuring

video guide by tplink: https://www.youtube.com/watch?v=j4M8F0WRYV0
(for XE75 model but its the same for all)

then, you just pair the other deco nodes to the main one with the app and then just put them where you want

I have no recommendations.