Yes! You are not alone. Now that my gf and I have been in a committed relationship for over 3 years now, this issue is affecting me more and more. Unlike those young, frantic, short-term relationships where you might be in bed together only for sex, we're at that more mature stage where we want to have our sex and get some sleep too. We don't live together and, given our schedules right now, we don't spend every night together. It sucks to be together so little, but the one upside is I at least get a good night's sleep a few nights a week. We will probably get married someday, and I have already decided that a king-sized bed will be a must when that happens. We have spent some nights in hotels with king-sized beds, and I found it made a world of difference.
There was actually a Seinfeld episode about this in which Kramer discovered the wonders of George's parents' twin beds after losing sleep being in the same bed with his gf for several nights. I believe this comfort factor--more than prudery--really explains the popularity of twin beds in the 50's, and the popularity of king beds today.