If you fit shelves to load bearing walls it will be fine. But not internal walls made of plaster board.

 

Load bearing walls are the ones that don't sound hollow when you tap them, right? (Can you tell I know nothing about this sort of thing? ). So I should be ok with the wall that joins my flat with my neighbour which is the main one I'd want to utilise

 

Yes, you usually get a dull sort of sound when you tap a solid (load bearing) wall. If you are in a purpose built apartment block (as opposed to a house divided into flats) I would expect there to be a solid wall between you and your neighbour.

 

Probably best to use external walls if you are unsure. My new extension walls are OK for paintings. The wall between you and next door if the floor joists sit on it is load bearing. Floorboards run in the opposite direction to floor joists.

 

I have no idea about joists. When I tap on the wall between myself and my neighbour it sounds solid and load bearing (the internal walls sound hollow when tapped). That's the main wall I want to use. I want to put some shelves and ramps near the cat tree so that they have one big climbing area. It is purpose built block of flats.

 

It might be worth seeing if there is a DIY type man ( or woman! ) locally who can do this work for you. Part of the problem is having a decent drill and knowing which kind of drill bit to use. Also it is necessary to check there are no pipes or wires running through that patch of wall!
Try local FB pages or Streetlife for recommendations, it shouldn't be too pricey but you are more likely to end up with solid fixings.