My 2 sheckels worth...use your ratchet straps for now...you can worry about better suspension in the spring.
At the moment, you need some insulation. I have to agree with the CCF pad from WallyWorld. One option no one has mentioned is watch the WallyWorld and catch a sleeping bag for $10 and change with free shipping. I for a 40 degree bag last week and modded it into a top quilt. If you don't sew just unzip it about 3/4s of the way down and pull it over. A safety pin can hold the zipper slide in place if it moves too much. The $10 bags are heavy but if you're car camping and weight and bulk aren't an issue...they'll work just fine.
I'll also agree with a cheap blue tarp from WallyWorld...I've modded a few to make them a bit more robust but its not absolutely necessary.
Sounds like for about $25 give or take a couple of bucks you could set yourself up with insulation and cover then save up for suspension later...