Mesh AP Recommendations

Hi all. I have a Linksys WRT 3200ACM running OpenWRT, and as many have mentioned on the boards it has some wifi issues. It's mostly working OK, but the signal just seems to drop in and out sometimes and it's all a bit inconsistent. I don't have a massive house, but it also seems to struggle to cover the house and garden. The wired side seems fine.

I am thinking of just switching the wifi off and getting multiple APs to cover the whole house, and maybe one outside for the garden. So, I'm guessing mesh is the way to go? Can anyone recommend some good hardware to do this please? It doesn't have to run OpenWRT because the 3200ACM will be between it and the Internet, so the stock firmware is OK if it's any good.

My main requirements are that it can support a 5Ghz and 2.4Ghz network with access to the rest of the LAN, and another 2.4Ghz guest network that has access only to the Internet. I'm guessing that means it should support tagging so that I can do the routing via the 3200ACM in OpenWRT.

Any help is much appreciated.