Ah cool! You’ve got a decent budget and not many ‘needs’, which makes things easier. It kind of depends on what your preferred ‘sound’ is like of course, however I always like to base my amplification on whatever has been used to voice the speakers during testing. Now interestingly, B&W (at least the 600 series) were historically voiced with Rotel amps, which are a really nice choice for your application I would suggest. Not too expensive, something relatively slim. Honestly I’d give something like the A8 a listen and see how it pairs with your B&Ws, at only £400 it might do everything you need and save you a bit of money.
https://www.whathifi.com/reviews/rotel-a8