I see. I will still not recommend Deco X20 in this case since you do not have LAN ports in the rooms.
But if you really have budget constraints, just go ahead and it may work for you with three pack solution (Challenger listed price is at S$269 for Deco X20 3-pack), say one in the living room ONT area, one in Bedroom 3 and one in Bedroom 2, speed will not be good for your PC but it may work. Main bedroom will be even worse. You can also carry out the experimentation to see which arrangement gets you the best results.
I believe Deco PX50 three-pack may be a good solution if your budget allows, speed will not be great but should be much more stable than Deco X20. It is using G.hn G1500 Powerline Network for backhaul, say one unit in the living room ONT area, one in Bedroom 2 for your PC, and one in the main bedroom. You can consider Powerline backhaul as a "pesudo Ethernet backhaul with lower speed" and it will much more stable than wireless backhaul. Challenger listed price for three-pack is at S$499.
https://www.tp-link.com/sg/home-networking/deco/deco-px50/v1 (3-pack)/