In 2015 we experimented with using a mouse to track position for our kiwi drive but we found that even with a gaming mouse that had a fast refresh rate we still couldn't get accurate distance measurements when driving on the field. We ended up using an encoder on each wheel and a gyro to track our x,y position on the field but we had to be careful and not accelerate too fast or the wheels would slip and we would lose our position. A mecanum drive would also have similar problems with wheels slipping so you might want to implement some acceleration control or for a quick solution just slowly ramp up the power when you first start moving which is what we did in our 2015 code posted here
https://www.chiefdelphi.com/media/papers/3180?