I found front opening PJ tops with short sleeves very comfortable (try Sussan). Comfy, knit elastic waisted pants are also good (Myer intimate apparel dept had some in navy and grey which were great). You will likely be in a gown before and after surgery but they may shower you pretty much the day or second day after surgery and then it's nice to put on fresh clothes. You may have a drain in (I did but that was for a mastectomy) but you don't need special tops to accommodate that. I had a pair of soft slippers to walk around the ward once I was up, helpful if they have have a reasonable sole, non-slip. Air con may be a bit cool - I had a cardigan, again, front opening, but a nice shawl or wrap would do. All the best for your operation!