Hi and welcome!
Here and especially I think over on the 2s forum (which is a pretty active one--for wavy haired girls) there are a lot of fine haired ladies who use a Curly Girl or modified Curly Girl method to care for their hair.
If your hair is both fine and damaged, I think you can definitely get some benefit from this site as far as methods of getting moisture and protein into your hair--you should definitely try a protein treatment, like this one: PT recipe - as promised
Board wisdom says always follow a protein treatment with a deep moisture treatment unless you really feel like you don't need it, of course, which may be why you've had trouble in the past.
Deva products aren't too popular around here, not because they're hated exactly, but because for the price a lot of people seem to have found that there are other products they like better ... I personally tried their low-poo and it was THE. WORST. for my hair, but then again that was the final confirmation for me that protein and my hair don't mix!
Jessicurl on the other hand seems to be really popular, though I have no personal experience to add to that.
Basically I think if you want to see how much wave you can get out of your hair, you should go for it! If you want to wear it straight, having healthy, well-moisturized hair is still a good goal, and to me it sounds a lot like you would do well trying out some of the methods people on this site use.
Hang out, read up, see what you think.