[Advice] Wireless Mesh only Setup

Hey everyone,

I'm looking to replace an ASUS RT-AX88U that has become a "restart-required-hourly" brick. I've had bad luck with ASUS hardware longevity and I'm looking for a new solution.

The situation:

• ISP: Vodafone Cable Germany (250/25 Mbps). No upgrades planned.
• Layout: One-story falt. Modem at one far end; gaming PC/office at the other (~25m) (modem and ASUS router down the hallway about 18 meters away with line of sight, uses 5Ghz Band with a link rate between 500 and 1000 Mbps and an RSSI of -50 to -55dBM)
• No Wires: It's a rental. Powerline is useless (10Mbps), MoCA is blocked by the ISP and ethernet runs are not parent-approved
• Placement: Ideally Desktop. No ceiling mounting
• Modem: ISP Provided, cannot be set into bridge mode (I am aware of double NAT)

Since I'd like to have more control of my network (what the ISP modem does not provide) and a separate network for smart home / IoT devices I was thinking about using Unifi.

I've seen reviews and setups with Express 7's or UDR7 + UX7 meshed with wireless backhaul, which (even for lack of a dedicated backhaul channel) seem to work well.

I also thought of maybe going with a Cloud Gateway Ultra and two U6-Mesh. I've seen reports of them burning up (albeit with outside use) and generally being quite hot, therefore maybe U7 Wall instead? but it, again, has no dedicated band for meshing.

Why Unifi so far? As mentioned in the beginning, I am quite unhappy with the longevity of ASUS devices and don't want any features hidden behind subscriptions (i.e. eero). Going with a "proper" mesh system, like TP-Link Deco or Netgear Orbi would also be more expensive, with what seems no real benefits outside of (maybe) a dedicated backhaul channel.

I don't need Gigabit speeds in the network as I don't do any file transfers or similar. WiFi 7 is not a must, since all devices are WiFi 6 at best. Only my PC, which would be wired to the mesh satellite, supports WiFi 6E.

I know that mesh with wireless backhaul is not ideal, but in this case it is the last resort, to get even some kind of a usable internet connection on my end of the flat.

I'd love to hear your thoughts and appreciate the help!