Mammoth is ~8,000 ft, good elevation for sleeping, but you really should spend as much time as you can at higher elevation to acclimate during the day. I suggest day hiking up at the end of Rock Creek Rd above the little "town" called Tom's Place - just a few exits south of Mammoth off 395. At the end of the road is the trailhead to Little Lakes Valley, a perfect acclimation hike at around 10,000ft with very little climbing. You go by lake after lake surrounded by 13er's, then turn around whenever you want. We do this all the time, usually going back the next day. We found the second day becomes much much easier than the first day.
