A few additional remedies not previously mentioned:
- Get a big dog – if your girlfriend isn't "live-in", then it'll help to have someone else flopping around on the bed while she's away through acclimation, and possibly give you a good excuse to spend more dates that end "at her place", but which still require you to go home afterwards to "walk the pup".
- Get another bed – Seriously, if she is secure in your relationship, then having the option to sleep separately so you can get better rest won't offend her, and she may appreciate your less-crabby self in the mornings.
I know you said you don't want to stop sleeping with her, but if left unchecked, lack of sleep can start to cause real distance or animosity in relationships. If you truly love her, do not let your girlfriend be your excuse for why you can't get a good night's sleep.