Hi Karl,
I was in a similar position as I love my existing A200 Premium and struggled to find something else. I ordered a GLA when Merc were still on the scheme. However, I ultimately cancelled it due to there being no timeframe for when the GLA might come and I needed a larger car. I went for a Hyundai Tucson (Hyundai seem to have upped their game lately, interior-wise), but I note what you say about not wanting a 4×4-type replacement.
In your position, perhaps a BMW 1 Series, or 2 Series Gran Coupe? I can’t really see anything else of a similar class that would appeal if you have been used to the Merc. Golf perhaps? Not seen the DS4, but could be a good shout – photos look nice. Obviously, I would check the wait times on all of these given the chip issues.
Good luck!