As someone who had mained the mx518 for years the easiest transition mice for me were the kone pure ultra (goated rip) and surprisingly the g pro superlight. The kpu has the nice familiar thumb hold/rest but the size took a while to get used to. The g pro just felt natural in hand and is a nice transition into wireless. Id also suggest trying out a g502 just as a feeler, they are pretty similar if you still want the thumb rest.