Wow, thanks for all the info & feedback! You guys are awesome.
I like the rubber stopper idea, I think I'll try that (I have some cork chunks laying around that I think I can use) - although I have an extension table so I'll have to see how that works out. I also have a lot of parchment paper and vinyl on hand so I'll try those too! Might as well try all the 'free' options first!! I like the idea of sort of "tenting" the machine base so there aren't any corners for anything to catch on - I do tend to get hooked up on the edge of my extension table so even aside from the "slip" issue that will probably make my life a little easier.
I did make sure to set up my machine at the right height, I work at a computer all day too so I'm very "keen" on ergonomics and fully appreciate things like having a proper chair, good arm position, foot support, etc. I built a custom desk and set myself up pretty well in that department. I can piece for hours and feel fine, it's quilting specifically that gets to me.
Partially I think I might be clenching up because the quilting step makes me a little nervous (it's so visible!), but I think it's also just from the non-stop pushing of a heavy quilt around. I don't have enough space for a large table to spread out on so my quit ends up pretty bunched up and heavy-feeling. Gloves helped so I don't have to grab fitstfulls of fabric anymore but I still really feel it in my neck/shoulders because I have to push down and forward to keep up with the needle.
Maybe I just need to take breaks more. But that's no fun!