Sounds like the best plan. Highway 120 from Lee Vining through the Yosemite high country is beautiful, and you have the option of a side trip into Yosemite Valley - spectacular. Highway 108, Sonora Pass, is very pretty, but very narrow and slow.
Just after the Lee Vining turn-off at 120, there is an excellent deli, the Whoa Nellie Deli, at the Mobile gas station. The Tuolumne Meadows store will be open.
A couple of days ago I met another couple from the UK, while hiking the north fork of Big Pine Creek, who were following an itinerary back SFO to similar to yours, but with a side trip north of San Francisco to the Redwoods.
Have fun in the California sun! So much to see - come back again.
