First of all: congratulations, Mommy-to-be!
I've no idea what your financial situation is -being a single mother with no real support system- but if money's tight for you like it was (heck, still is) for me, you can always try what I did before investing in a RNP or bouncy seat - put him/her in the car seat base on the bathroom floor.
On my "travel system" (and probably on most), the bottom of the car seat is slightly curved and rocks easily on my uncarpeted floors. I attached an infant toy to the handle and left the handle up so he could interact with the dangling toy. When he became squirmy, he effectively started the base a-rockin' just enough to soothe him further. (Keep LO strapped in if you keep the handle up.) In fact, I still have yet to buy a bouncy seat of any kind because he just plain likes his car seat!
Certainly not the most desirable solution, but I thought I'd throw the idea out there just in case the immediate purchase of a rocker/bouncer/soother was beyond your means at the moment.
Best of luck to you!