Hi I need advise on my home Wifi network coverage in 1000sqft condo

Problem : In living room using 5Ghz network  I can get full speed 500mbps, but when I moved to Bedroom 2 or Master room I can only get <10% of the speed even with full Wifi signal with help from Mesh extender RE305 connected via WPS. Even with 2.4Ghz netowork I observed more than 50% drop in speed when I use it at bedroom 2 or master bedroom.

Current machine : Unifi provided D-link AX3000 @ Living room TV area marked in red
Extender : TP-link RE305 plugged at Bedroom 2 marked in red

I tried seek opinion from TP-link official store in Lazada, they suggested to me to get TP-Link Deco X20 or X50 2 units, 1 put next to main modem and another replacing the position in my bedroom 2, but before I actually invest in to this which may cost me about RM600+ anyone can give some opinion about this setup? I don't want to end up spent half k with no convincing result, I'm aiming at 80% speed at those dead zone if that is realistic.