When I was young, my hair was fine, but really dense. Age, thyroid and a medication I take have thinned it out. When I was shoulder length, my hair was "skimpy." Once I went to a chin length, inverted bob, it made it look like I had hair on my head once again. Unless you put in extensions, or do something like that, your hair won't look dense, especially when long.
Curl is another issue. Before I started lurking on nc.com, I never used products (or technique for that matter.) I read, read and read some more. Learned how to take care of my hair and maximize my curl. Went from winter wavy/summer 3a to hair like my signature picture all of the time. Can't guarantee more curl, but once you really learn about your hair and what to do--curl may or may not tighten.
Fine hair generally likes protein. I do at least one PT a week and use a lot of products with protein. I find that it tightens curl and reduces frizz.
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
HGs: Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; DM MiraCurls Curling Gelly; UFD Curly Magic; Shescentit LIs; Sevi conditioners; Botanical Spirits Puree, CJ Repair Me