Dear Kathie T.,
I agree with Aquanegra, that your scalp should be very healthy before you do anything extra to your hair.
If you do decide to go ahead, maybe your colorist can use a non-ammonia based product. I started highlights when my hair went mousy & limp, but I didn't go about it in the right way. (Eeeek!) I now use a colorist who charges twice as much but has made my hair look healthy.
I do get some serious breakage around the hairline during a flare, which is another thing to watch out for.
There are products out there that can add body that I'd never tried until I met this colorist. Maybe your hairdresser could also try some products on you until you find something you like? I have very fine hair & can use all the help that I can get, short of a perm---which I've done but with disastrous results. Talk about breakage!
Good luck! Hope you are making progress on the diagnosis front! Sincerely, Vee