Donna, I highly recommend getting front opening tops rather than pull over as you will not be able to raise your hands above your head for a short period. In addition with a mastectomy you will most likely have a drain tube so you will need something to carry the drain bulb in. Amazon has front opening shirts with inside pockets for holding a drain bulb.
Good wishes coming your way for your surgery and recovery.

The heart shaped pillow is great! It goes under your arm, and helps prevent too much arm pressure / friction against your surgical incisions. I kept another small pillow in the car for going under the seatbelt where it would cross the mastectomy side. I did not buy any special clothes, as I had plenty of button up, soft, cosy, pj tops. Other times, I wore my zip up hoodies!

I received a heart shaped pillow when I got my double mastectomy in 2017. It was especially helpful in keeping the seatbelt off my chest and I still use it to this day.

Donna, I use the heart shaped pillow to sleep as it prevents my arm from rubbing against the surgical site. It is also recommended to use in the car to prevent the seat belt from rubbing against the incisions and to protect the chest area. A friend gave me a "Ford support belt" which velcros to the car seat belt. I have been using that once I was able to drive myself and it is very comfortable. You can google it.
You may also want to check out a site called "Unite for her"and register. They sent me a very nice welcome basket (free) with very useful products.

Thank u I saw that. Also the dr gave me a small heart shape pillow is there something better I should get