IMHO, one really decent full-sized tripod is a better use of your initial tripod $$ than a table-top unit which limits you. You can use a full-sized tripod on a table. Just try to get a nice, light-weight one. I have a relatively low-priced carbon-fiber unit with a ball head and it works for me in those situations where I absolutely need a tripod. It's not sturdy enough for performance sports or really long lenses but it works for me both for formals and for 90% of my outdoor needs. And it's very light and not a burden to take with me.

Jim