I'm also VERY nearsighted. It's helpful to realize that it's really pretty tough to make soft contacts come out of your eyes underwater. It's possible I'm sure, but I've found that it's far from a sure thing that your contacts will come out if you open your eyes underwater. I've actually found the opposite ... it's far more likely that they won't go anyplace. When I open my eyes underwater without a mask, I don't open them all the way. Just open them about half way. Enough to see a bit. I've never lost a lense doing that. Also, hopefully you wear disposable lenses. I always bring a couple of spare pair of lenses and my glasses with me everytime I go diving. Every time, regardless of whether it's a quarry shore dive, lake boat dive, ocean boat dive or pool dive. While I have never lost a single lens, when I eventually lose one (it will happen eventually), I want to be prepared. I'm absolutely blind without them. I can hardly walk without running into things. Driving or doing further diving is absolutely out of the question. So I make sure I'm ready for that eventuallity.
I also carry a spare mask in a mask pocket on my harness waist belt on all open water dives. I don't carry a spare mask with me in the pool.