You don't really need too much for a WLE. The shower head is a good idea. I found it difficult to wash my hair the first couple of times. I had a sentinel node biopsy at the same time which definitely contributed to the discomfort.
Get some advice from your doctors about the painkiller situation, maybe panadol osteo could be good as it's a bit stronger. I didn't need ultra strong meds so you could be OK with that.
The most useful thing for me was an ice pack. Get a couple at the hospital. You need one in the freezer and one down your bra. If they offer you more than one at the hospital, accept it!
Do you have the (so not attractive!) Berlei post-surgery bra? You get it for free, mine was given to me by my breastcare nurse before surgery. You'll need to wear that for comfort afterwards.
I was given a leaflet at the hospital with exercises to do after surgery, and I was given a Zonta cushion (a small cushion that you can hang on your shoulder that you can tuck under your arm to keep your arm off your side) by a volunteer after surgery. They were both useful.
Get some food pre-cooked and in the freezer so you can take it easy for a week or two.
That's all I can think of at the moment. If something else occurs I'll let you know! All the very best with your surgery, K xox
PS Hey did you ever get an answer to your chemo question?