We don't have a boppy, but I was looking at them in Target the other day. We don't have an exersaucer, but we have something similar I think. It is a walker, but we removed the wheels, so it is just a little seat with toys and things attached. We call it the stander. We also have a jumper which I can use to keep her off her head. However, I'm lucky to get 10-15 minutes in either of them, and that's with me in sight the whole time, preferably sitting on the floor in front of her.
Tummy time is also difficult. Once she learned to roll over, it was pretty much all over. I put her down on her belly, then she does a push-up, drops an arm, and rolls. After about the third time, she's had enough. I've tried propping her up on a rolled towel, and I can get a few more minutes that way because she can't roll over as easily.
She does ok with supported sitting, but I am the support. If you set her down against the back of the sofa, she'd topple over. I am beginning to wonder if her lack of rolls aren't contributing to the problem. Her bum is to scrawny to balance on.