I have experience with Google, Linksys, and ASUS mesh systems (I use ASUS), and respect Netgear also. Given your farily high number of connected devices, I would recommend a newer model, probably tri-band using WiFi 6 (not WiFi 6E) using 3 nodes (one for the main router and one each for the top floor and the garden). Many years ago I was involved in building routers, and even then, the more devices you have connected, the more your router needs good specifications so it does not cause your network to be slow.
I have put together a Linksys Velop system, but prefer ASUS Ai Mesh for the no-cost security. Again, depending on budget, their AX8 system has proved very reliable at a friend’s house across 4 floors, all with wireless connections to each node. We have separated the 2.4 GHz and 5 GHz bands to provide more control over what devices connect to each band.
I am expecting that your internet service provider allows connecting a second router to their router (I have AT&T in the US and they allow me to do so). Best to confirm if you are planning to make a change. PM me if you would like to have more information.