How do I bathroom / kitchen / extension? etc.

TBH I wouldn't bother, more hassle and compromise than its worth, get a good portable speaker and take it everywhere.

I looked at it then realised that the fancy ones go out of date pretty quickly and the others are just a really expensive bluetooth speaker that don't sound very good so I got a rechargeable DAB radio.

Sonos Move

We don't have a soundsystem but we have speakers - two of these in our bathroom ceiling, with speaker cable running to our kitchen hi-fi (bathroom is off kitchen). Cost £200 for the speakers + cable, definitely worth it.

They aren't big speakers and work fine in our very small bathroom but you'd need bigger in a bigger space.

I'd do the same thing again, if we want to control the sound in the bathroom we cast to the hi-fi and use our phones as remotes. For me being able to listen to music or a podcast in the bath is important...

Used to have in-ceiling speakers attached to an original Sonos ZP100 that was in the loft. Speakers are relatively future-proof so once they're installed, you can always update whatever is connected to them.

Built in soundsystems for bathrooms

Depends on the space. My mate did it (DIY) in a top floor flat with loft above in two of his flats. Pretty much the same set up as fox. Both were small bathrooms so he just had a single speaker iirc. Can't remember about the first, but in the second place they definitely had volume controls next to the light switch.

Less hassle than a celling extractor fan. Would definitely recommend.