I had a single mastectomy without reconstruction in 2020. I did buy one of the Nicola Jane bras but it didn’t suit my body shape. Instead I bought more of the sports bras I knew I found comfortable. I now wear stretchy t-shirt bras from Sainsbury’s as I don’t have any kind of prosthetic.
I would recommend a heart cushion. I still use mine at night. Mine came from some kind of Cancer Research fundraiser that my mother in law went to. If you can sew a bit there are patterns available online.
I had a drain fitted and it came in a little cloth shoulder bag. Not all hospitals provide this, so definitely something to check as Tulip says.
Wishing you all the best with the operation