You both are confusing mesh with roaming. What you need is some AP that can do 802.11r (fast-transition) aka roaming. You can just set up two access points with the same name and the phone will connect to the nearby one just fine but connections will drop upon change, whilst if you enable roaming you could walk around the house during a call and at most suffer a little stutter of a few milliseconds. Any router/AP supported by OpenWRT can do roaming. Don't use these so-called boosters, they'll reduce your bandwidth in half at best.

I don't know how old your current setup is, but router tech improves crazy fast like everything else. If you shop around for mesh wifi systems now, I'd guess you'd struggle to find anything >5 years old.