This i5 would be perfect spec: https://www.autotrader.co.uk/car-details/202601099024700
That is interesting. I'd take it over the i4, the comfort seats alone are incredible.
In terms of quality, it's a bit hit and miss but I'd rank it above an i4. The glass lighting trim really helps the interior and the 520i you tried wouldn't have had it. Things like the window switches are a bit of a disappointment though.
Could be worth a look but ultimately if you're happy with an i4, they're a solid car.