There's only a few states that are truly OTC for mule deer. Idaho for rifle, Arizona has great opportunity if you're willing to archery hunt. Wyoming and Colorado require draw applications. Although some units are guaranteed draw.
Check out a local pro shop. Otherwise all arrow manufactures have charts on their websites that get you in the right ballpark. If anything, lean towards the stiffer side if you're on the edge. It's easier to add weight upfront imo. I love my black eagle rampages