Easiest route in Yellowstone Park for 1st Time RVer

Wow my first post and so much valuable info! After evaluating some suggestions we may delete Cody as a stop. Too out of the way. Thinking now when leaving Yellowstone to take 191 to I90 into Billings then take I90 on through Buffalo toward Mount Rushmore area. By deleting Cody this will allow for some time in the Jackson/Teton area. Still evaluating about going the route through Idaho Falls then north after seeing Jackson/Teton area. Great to know what roads to avoid!