We have ten weapons in the game and some would like to be able to switch between them easily and on the fly.

This is merely a suggestion off what you could build your conventional WSAD control scheme. I ve tried putting all weapons as close as possible to WSAD.

WSAD movement (and i use Q for crouch, space for jump)

pistol - 1
BFG - 2

shotgun - Z
machinegun - X
plasma gun - C
gauss rifle - V

melee attack - F
chainsaw - G

rocket launcher - E
super shotgun - R
chaingun - T

If you dont use Q for crouch (probably can be used for something else because crouch is not very important in doom), you can use it for a weapon, too.

I have item use and switch on thumb mouse 1 and 2 and weapon special at mouse 2 as by default.