Hi Elisabeth. I got your message We had a great trip to those states last summer and spent three weeks doing a long loop. We started in Jackson, WY and went to Yosemite for a few days and then up to Glacier National park before heading south through the edge of Idaho. We spent three weeks altogether with several stops of two or three nights. Yosemite is an obvious place to go, but if anything we liked the rugged beauty and relative quiet of Glacier even better. The Tetons near Jackson are also spectacular. In between are some great old western towns - and ghost towns. We chose to stay off the highway and in the big open spaces. If you go in the summer, try to find a local rodeo (many of the schedules are online). We caught one in Augusta (which is a tiny place), and it was well worth the detour. I have a Google map which has most of our highlights. If you email me at email@example.com I can send you the link (it won't work through this system).
All the best