My wireless mouse (Magic Mouse 1) is always loosing contact with my MacBook Pro. It is the worst Apple product I own. Hopefully they solved the problem with Magic Mouse 2.
The problem with MM2 is that instead of replaceable batteries it has rechargeable built-in batteries (which will degrade over time) and the recharging socket is ON THE BOTTOM so you cannot recharge and use the mouse at the same time. That was the reason I bought the old version. What a mistake!
I bought a spare Mighty Mouse (the one with the scroll ball) before they all disappeared. It's still sitting in its box awaiting my needing to use it. The only issue I have with these mice is that finger grease tends, over time, to attract dirt to the rollers the scroll ball moves. Rubbing (upside down) vigorously on a denim-clad thigh(!) usually cleans them but if not, even though they are not designed to come apart, it is possible with care which is how I've kept mine going so long.
I doubt you could buy one now and I'm not selling mine ;-) Dare I suggest you consider a USB mouse from a different manufacturer?