For anyone experiencing this problem using a second monitor, I have just switched the side my monitor was on from the right of the mac book to the left and it seems to have drastically improved my RF issues. Turns out the bluetooth module is on the left of the laptop, so it keeps it more central and closer to the mouse I guess. Also my dongle for the monitor is now plugged into the right of the laptop, instead of the left which may also have had an effect.
Still early days but two days down and no connection issues from the mouse.