Small Footprint SS Power Amps

Many small-shop monoblocks using PuriFi or NCore modules would fit your description. Some well-known vendors are Nord in the UK, Apollon in Slovenia, and VTV in the US.
These are class D but I would not rule them out for that reason. I replaced a more expensive AB amp with PuriFi monoblocks and haven't looked back.

Go  by sound not size.

Maybe the AGD GaN amps. There is a thread on them.

BTW - I have 2 AHB2’s hidden in my sons IKEA toy shelf which are 12 inches wide. A perfect fit.

Schiit Vidar

My new (to me)  Herron M1 monoblocks are pretty awesome. Small footprint, 150 WPC, but you need two.