Yes, the wall knocking down exercise requires Building Control approval if the wall is a load-bearing wall. You need proper advice about this. If you ask a couple of builders and they both say, yes it's loadbearing but they will just put a lintel in, alarm bells should start ringing - such work MUST have BC approval first.
The answer to your question isn't straightforward I'm afraid. The recent rush towards use of wood-type flooring has caused all sorts of problems for downstairs neighbours in flats that many leasehold and freehold flats have constraints on them to prevent the fitting of such surfaces. The very action of fitting such a flooring reduces the sound-deadening properties between the 2 dwellings. It may be acceptable to fit cushion flooring if that is acceptable to you, or laminate on a 'floating' substrate - using what is effectively a large sheet of doublewrap under the floor to act as a sound deadening layer.