You didn't say what the capacity of your SSD is but it must be really small for you to have that much of a problem. Anything over 60GB should be fine for any version of Win7 without much trouble. Anything under 40GB might take some diligence to keep your C: drive uncluttered in Win7.
Back in the early days of SSD-based netbooks when SLC NAND was expensive and MLC was too slow, many of us had to deal with installing WinXP to a 2GB SLC boot SSD with as much as possible on a slower secondary drive like an MLC SSD or an SD card.
Many people butchered XP with nlite to make it as small as possible but with a little care I found that unnecessary. I ran a full installation of WinXPpro and most of my apps in less than 3GB of the 4GB boot SSD in my EeePC901.
All my bulk data, document folders, temp folders, etc and many of my program files went on the D: drive.
If you check over at the eeeuser.com forums you'll find lots of tips for saving space on your OS drive.
One important consideration is your pagefile. Windows wants to make it the size of your total system RAM by default which can be pretty ridiculous in a modern system with loads of cheap RAM and a small expensive boot SSD. Reducing it from a Windows-managed 8GB or 16GB to a static 2048MB will free up from 6GB to 14GB of precious SSD space.
It's been years since I've booted from a mechanical HDD. They're just too slow. I hate to hear you talk about abandoning SSDs.