There will be plenty of options in mid-July, though some of them won't be the usual bets for that timeframe. There's a good chance you'll be able to see some Salmonflies.
In detail: Parks' Fly Shop and Yellowstone Fisheries News
Firehole: AM better, probably. White Miller caddis and PMD.
Madison: similar to Firehole, but will fish all day.
Gibbon: Drakes in the meadows late AM, attractors in the canyon PM.
Gardner: Salmonflies, either nymph or dry, plus smaller attractors, caddis, and flashy attractor nymphs.
Lakes: all except probably Yellowstone and Lewis/Shoshone will be fishing well. Flashy beadheads, soft hackles, Callibaetis, damselflies, maybe a few big caddis. Big draws of park lakes are grayling in Grebe, Cascade, and Wolf.
Gallatin: still high but dropping. Probably a nymph show.
Slough Creek: streamers in the lower meadow. Lots of mosquitoes. Maybe some drakes. Upper meadows probably still too high.
Soda Butte/Lamar: probably still too high.
Yellowstone: probably still too high.