Stock tyres are Michelin 185 60 r15. I am looking for softer tyres for a comfier diving. Will it work to install a bigger tyre on the same r15 - the 205 55 r15 which is 20mm wider - or - the 205 60 r15 which is also 24mm higher? Visually there is plenty of space around stock wheels but I am worried that new tyres would not rub.

 

If you want soft, try Continental. What I have heard, also Pirelli or Bridgestone might be softer, but I don't have personal experience of those.

In general lower profile provides more precise control and less comfort, and vice versa, higher profile gives less precise but more comfortable ride. Therefore for softer and more comfortable ride I would try 185/65R15.