FWIW, there's a similar thread here:
Buying Advice 15" MBA vs 14" MBP
I've agonized over this. Before this year I'd never bought a laptop for myself and didn't much enjoy using them. Earlier this year I bought an on-sale base model M1 MBA (8/256) to see if working on the floor would relieve the lower back pain I get when sitting at a desk too long. For that purpose, it worked very well. But, it's not quite enough machine for me.
In an attempt to improve things I put together an external 1TB SSD (Samsung 970 EVO Plus) and made it a boot drive. That improved things quite a bit, but it turns out to be a real PITA to be tethered to a hot SSD while working on the floor.
So, what next? I like the idea of the larger 15" screen on the MBA (16/512), but would I find it awkward to balance something that large on my lap while sitting on the floor? For just a bit more money I could get the 14" M3 MBP (16/512), but that seems a bit heavy and bulky for real laptop use. On the other hand, the better performance and stunning display are impossible to ignore.
It's a tough one.