I use Player:GetMouse() regularly, so because UserInputService can print if the player presses a key, is it possible to get the mouse in UserInputService?
Mouse has been superseded by User Input Service. This means the functionality of the aforementioned Roblox Service is one that is widely accepted than its legacy counterpart.
You are being provided with the full document: https://developer.roblox.com/api-reference/enum/UserInputType