Lots of stereos from other VAG cars will fit.
RNS310,RCD510,RNS510 Loads of info out there on these. You might also need to update your Can Gateway if you fit one of these as they can cause the battery to drain.
There's also some Kenwood headunits designed to fix but are expensive £600+
The other option is a Chinese Android system at about £300, reviews are mixed on these. I have one, and its ok. Not great, not awful.