I went for a year or so w/o CO2. My plants didn't die, but they sure didn't thrive.
Having switched to DIY CO2, it is SO cheap and easy, and the results have been SO incredible, I feel foolish for not having done it before. Just get some juice or soda, some tubing, sugar and yeast. I have had no leakage w/o adhesives simply drilling the holes smaller than the tubing.
With a 10g, I'd suggest you pick one kind of tetra - at most 2, and school them. I have always found serpae extremely hardy (and cheap!). Otos are always good in a planted tank. And a couple of cories. For color and flash you could add a pair of betta, tho some folks have found erpae to be nippy. Neons and glow-lites are probably less so, and sure flash nicely in schools.