The ZyXel WSM20 (also branded Multy M1) is available pretty cheaply in a 3 pack (£90/€100).
It has WiFi 6 @ 1800, MT7621 dual core, 128MB flash, 256MB RAM, 4x gigabit Ethernet (including the WAN port). It’s sold as a mesh system. Support available on master.
The main limitation for you (which applies to all hw in your spec) will be that 1200 WiFi won’t come close to saturating a 1200 WAN - you’ll likely max out at about half, and the mesh backhaul will eat some of that too. In fact as the WAN port is 1Gbps you won’t be able to max out even with wired clients.
Gigabit plus internet requires pretty beefy hardware if you want to max it out. My question is, do you need to max it out? If so you’ll need to invest. If not then 500Mbps symmetric is plenty for a family streaming multiple 4k movies while also online gaming. I’d suggest reading