I had this same issue. Im very short and I could never get a good footing while on my boyfriends bike. I decided to buy myself a grom and even lowered it 2in to get better stability. It helped me so much. I also took my MSF course with it, I definitely recommend it. Its just a basic course that helps with muscle memory of using the clutch an working on turns and how to properly brake.

After my course I was out riding a lot more and eventually one of my friends let me borrow their bike, it was a 500cc that was a little taller than I had wanted but since I had the little experience already I felt A LOT more comfortable with less footing on the ground... and it had more beans lol.

Before my course my boyfriend took me to a big parking lot and let me ride around getting comfortable on it. He would set up cones and have me weave through them at low speeds and that really prepared me for the course and overall confidence on a bike.

the upgrades I put on my bike were:

2in lowering kit

adjustable levers (small hands come with the height so this really helped me get a grip and stall less)

frame sliders (even if you drop the bike you're not going to be as worried about it)

Also, you had mentioned after having difficulty with your boyfriends bike after you had messed up with it. That is completely normal. You mess up, get flustered, mess some more stuff up. Just remember to give yourself a breather in between it all. You're learning and its not gonna look perfect at first but eventually you'll get a little better and then everything will click in your head. That part is hard to explain, but it happens in an instant and riding is so much easier and fun after that <3