Hey @Ulli,
I had breast conserving surgery as well. I am not sure how long it is since you had yours, but as I had chemo as well there was 8 months between surgery and radiation. Even though there was still up and down swelling I was back into a normal bra by then. I just poked a bit of tissue or gauze between the wire and me when it started getting a bit sore. Cotton wool can stick a bit if it starts to get weepy.
You might try one of the ones with no wire that open at the front or I found the little crop top ones from Best and Less pretty good. They even held up riding my horse so should be fine for walking.
I had 6 weeks of radiation and had no problem with fatigue throughout. I had very little burning until mid way through week 5. Get on to the Moo Goo udder cream if you haven't already. Moisturize moisturize moisturize.
All the best lovely.
xoxoxo