Hi Julie
I had a few ops and I just wore PJ's in hospital - ones with a button up front or stretchy enough for the doc & nurses to check my breast. When I got home I just wore a crop top or fitted singlet under my clothes. When I felt comfortable to wear a bra I wore one of my old stretched ones and took the wire out of that side. After my mastectomy I wore post op bras. While in hospital you should be seen by a breast care nurse who will advise you on what you need. She will also order you a my care kit - http://www.bcna.org.au/about-bcna/information-health-care-professionals/kits-and-resources#mck
It really depends what surgery you are having.
Good Luck with everything
Ann-Marie x