I adopted a "brace position" for Space Mtn that I actually enjoyed for all coasters: Fingers interlocked behind my head, elbows forward. This gave my head a little support and cushioning from side-to-side jerking forces, and also served a similar purpose to why people put their hands up on coasters, the added thrill of a "Look ma, no hands" feeling. (Obviously not relevant to OP, but relevant to the skeletal suffering.)
To the OP, I'd point out the Disney is the
perfect place for you since it's not just a bunch of crazy roller coasters where the only point is the G-forces; it's a land of imagination and theming. You do you, you do your Disney, and if you worry that you're missing out on some of the fun, follow the same kind of regimen that's prescribed for kids who are a bit intimidated by coasters. Seriously, like start with Barnstormer. I think
maybe I might make the second be Slinky Dog (during the daytime) rather than Seven Dwarfs. For Slinky Dog, the whole coaster is "out in the open," and you can see all the track. It's fairly gentle on you physically. For Seven Dwarfs, it's true that it's broken up with "dark ride" animatronic elements, but the whole thing could be a touch more intimidating for someone uncertain about coasters. The initial "climb" is inside the mine, so you can't see what's coming.
In any case, if you want to take the plunge (hehe), go for a seat near the front. On any coaster, this will mean that when you go over a drop your change in velocity is more gentle (
https://jacobsphysics.blogspot.com/2011/01/do-you-go-faster-if-you-ride-in-back.html).