I have this problem for a while now, and it's starting to really piss me off. Every time I play an OSU beatmap, everything is fine, but later on I start to slightly lift my mouse up and eventually the mouse starts jumping around the screen causing me to fail the beatmap.

It's also extremely hard to put the mouse down again after lifting slightly up.

Is there any way to stop myself from lifting my mouse up? Or would I need to buy a new mouse?

I would suggest buying a new mouse with a top optical sensor (e.g. Pmw3310/3360) WITH low lift off distance (somewhere between 1-2mm would be nice)

I would say 1 add more weight if you can, some mice allow weight customization. Aside from that my best guess is that you might be tensing up you shoulder causing the mouse to get lifted, if that's the case try relaxing. If neither of those recommendations are of use maybe try a different grip, if you are palm try claw.

A few options I could suggest;

1. Weights: if the mouse is light or such sometimes it can be easy to pick it up, and causing your problem, however it could take a slight adjustment period. But if it solves your problem, great!

2. Mouse positioning: Now this one can kind of be tricky, but if your mouse is an awkward spot or in a place you're having this issue, try moving your mouse completely around your desk until this problem doesn't occur, and again there will be a more labor intensive option, but I've seen it work.

3. A mouse with a high lift off sensor: Mine has a customization option to where I can set how harsh the lift off is, some people don't have that option, nor have I toyed with it, but again I have seen it fix some people's problem before.

4. Mouse sensitivity: This one is probably the most labor intensive option if your problem becomes so unbearable it might be worth investing in, but switch your mouse sensitivity to something more sensitive, so you don't have to move your hand/wrist so much, which is usually the problem in this case. There is usually a really big adjustment period if you go with this option depending on sensitivity adjustment. DPI is usually the best adjustment, but Osu has it's own adjuster in the settings tab. Again this can be really tricky to fine tune and if you can fix it otherwise it's usually easier.

5. Hand positioning: If your hand position is light or resting it can slip or you can pick it up, causing connection loss. Try changing it up, or just buying/using a new mouse completely, the ergonomics can really make or break the mouse sometimes.

6. If all else fails, try a decent mouse pad and re-train yourself to play with mouse and avoid lifting it up. This seems like a really obvious solution, but if nothing else is working or you're out of options, sometimes it can be user error and the only option left.

I had this problem too being a mouse only player. I can only tell what worked for me and it did work.
#1 Buy a new mouse,
I bought a bigger mouse so my big hands could grip it better and no more lift off problems since.
#2 Change grip style, this is what I did before the new mouse. Hold your mouse with your finger tips making contact with your mouse not the whole finger? Like a claw grip but I still had my palm on my mouse. Just dnt ever lay your fingers down on the mouse you'll get used to it, worked for me until I layed my fingers down. Hope this helps. Mouse Life <3