I have always slept on my side before. Also they never really hurt like so many talk about, more of an achy burn. Inactivity, like sleeping, is fine but when I would start to move again, ouch! Ouch! Ouch! That hasn't happened very much in a while either. And no nipple sensitivity either. I would torture my boyfriend by straddling him while he is sitting on the sofa and put his head under my shirt, wait for him to get all hot and hard then just hop up and go do something else. It didn't do anything for me, well the grinding did but not the breast play, so no problemo.
Now over three years in on hrt things are different. Working nightshift, I will occasionally take a nap in the early afternoon on Saturday and I have to lay on my stomach so my hair doesn't get messed up. The C cup breasts do not like that at all, I lay with two pillows from my hips to my boobs and then a throw pillow under my face. They settle perfectly on the bed with no pressure. Sometimes one of my hands fall asleep or my bf wakes me up to go somewhere and I have giant lines on my face that do not go away for an hour but other than that it works well. I also have pain now if anything catches a nipple, like almost tears pain. And the whole torture the boyfriend thing has gone full circle. There is some direct connection from my nipples down to my groin, I mean, oh My GOD! and he is merciless. I still straddle him, sometimes to play and sometimes to get his full attention. I have to take his attention off the game or the history channel or the news, seriously when I ask how I look he could at least look up from the television before he says, "You look great sweetie."

Anyway he goes to them right away to shut me up and I have to run away, or at that point it is usually stumble away. Is that humiliating or what?!? This morning I am giving him crap because he never closes doors or drawers while I, who takes muuuuuccccchhhh longer to get ready by the way, am bending over closing them he comes up from behind and starts grinding on me. When that didn't stop me from reading him the riot act he reached around to my boobs. Grr! So now I am bent over, vacantly staring at the open drawer, not able to breath right and he is blissfully back to brushing his teeth to the sound of my silence.

He may be pure evil.
It is possible to be comfortable, you may just have to experiment a little.