Remember that holding both mouse buttons down moves you forward as well.

I use only keyboard and a regular-buttoned mouse (mmo mice are too heavy for my preference). I play rogue, outlaw and sub, for my main character, and I can tell you I have a million keybinds.

• bind all the keys around wasd. They’re prime estate. Even x. You can bind sit to shift x if you really want a sit button.
• maximize your use of macros. I use bindpad which lets you make macros right in it and bind keys directly but there are a lot of other addons too that let you make as many macros as you need. Macros let you bind multiple spells to prime hotkeys and just press a modifier to change it, or even have a different in combat and out of combat use for the same key (ex. I have sap and gouge bound to the same key).

I will say your hands hurting so much sounds pretty concerning, and I’m not sure a regular keyboard and mouse will relieve it that much. Maybe look for ergonomic keyboards and mice that are specifically designed to make your wrists not have to angle sharply, but just rest naturally.