You can use the OEM GM mirror switch as i believe the door mirror switch panel already has the mounting provisions for the mirror switch on the back side of it, you will just need to use a hole saw to cut the hole through the panel. Standard Motor Products part #DS1396 is one of the switches you can use and if you look on Rock Auto there are several switches on there from other manufacturers. GM #PT709 is the wiring connector to fit this switch. If you have the GM part number off of the factory gm wiring diagram you can search on mouser.com and find this connector much cheaper but you will need to assemble the connector.
The 2 tabs between the speaker and the power window switch cut outs are the tabs that the GM switch snaps into in the attached picture.