Info from my breast cancer nurse. No underwires.
Target sell post surgery bras, some very soft ones, not hugely supportive, but soft enough not to rub your sore areas. They have pockets for your soft form too.
Get the fitter to help you, or at least try them on, I found the sizes a bit on the small side.
Has the breast care nurse organised a Care pack for you?
It contains a Berlei post surgery bra, a soft form, DVD of post surgery exercises, and a VIP card for 50% off Berlei post surgery bras.
Myer sell mastectomy bras, they have a small range, but a couple are pretty.
If you google mastectomy bras, there are quite a few online sellers, I haven't tried them yet as I am not sure of my size. They have prettier ones than those in the shops.
If the bras rub, try wearing a dressing pad under the bra where your stitches are, I had to wear one for several weeks until it stopped hurting, but I had a reduction, so the scars were under my breasts where the band went.