@above, he said no mods, SPC is a mod
My method is 100% vanilla.
If your reading level was any better than a first grader, you'd notice he said he doesn't care if it requires a mod, not that he doesn't want to use a mod.
Edit: Ohh, I apologize. I just noticed he said he doesn't want to have to use mods to fly and ****. You must have confused that with him saying he doesn't want to use mods to switch the game modes. Okay. Now, there I don't blame you too much. That is a pretty good solution.
As a suggestion to you, K1LL3RSN1P3R65, Single Player Commands fly mode is a lot better than vanilla creative fly. Creative mode fly is rather slippery. Plus, with SPC, you can make it easier to turn on and off. Just set a bind to a key so that when you press it it will toggle fly on/off. To do this, use 'bind <key> fly'. I usually use the V key because in GMOD, that is the default toggle key for Noclip. (Or atleast I think it is...) Oh! And if you like vanilla fly because it is fast travel, with SPC you can just enter in the command 'fly <speed>' (Example:'fly 3')