If your current valve size is 3/4" then you should buy a 3/4" Fortrezz valve - that is a very common size for a residential cold water supply pipe. While you could use a 1" valve with 3/4" pipe your plumber would have to install a pipe size adapter on both sides of the valve, and you wouldn’t gain anything by doing that.
The size of the valve you need is based on the nominal size of the pipe leading to and away from it. Copper pipe with a nominal size of 3/4" has an outside diameter of 7/8 of an inch - you can measure the diameter of the pipe feeding your valve to double check your installation.
Note - you might want to edit the name of the picture you posted to something that isn’t your home address.