I would take a buggy though, it doesn't for part of any luggage allowance- nothing better than baby sleeping and you being unburdene! We went to Amsterdam and as DS1 hated the travel cot in the hotel we need it for him to sleep in as by 4am we were desperate for sleep!
We did Barcelona when DS1 was 6m. (now 8yrs) it was fab - everyine was very friendly, lovely place to sit out and have a few drinks/tapas etc - in one restaurant the waiter even took him so I could eat my meal!!
It was in feb we went and was warm and lovely - we flew back to snow. Don't know if it will be too hot in May/June.
Otherwise, I live in Germany and can recommend some of the NW german cities - Cologne/Dusseldorf are nice - also think about Hamburg or Bremen. No probs BFing - I did all over with mine and no-one batted an eyelid (nor did they in Barcelona)
Also within your flight range would be somewhere like Prague / Munich / Vienna etc - all very nice but prob best done now as not really 'small child' friendly - i.e. best to wait till they're 8-10ish to do again.
Dd is 6 weeks old and we were thinking it would be fun to take a little sightseeing break while she's still so portable. We have a sling which she sleeps v happily in, so no need for a buggy. Off we go! But where?
We'd like somewhere pleasantly warm but not crazily crowded or boiling in late May -- mid June, no more than 3hr flight from London, where breastfeeding in public won't be a problem. Suggestions please (would also appreciate warnings of places to avoid)!