M.S.
i wouldn't worry too much, if he is 7 1/2 m.o. and weighs 23 pounds and is a growing happy boy than I think you're doing things right. peiole who bottle feed (whether formula or breastmilk) get hung up on the numbers too much... if you are still nursing 3 times beyond his two bottles, he is probably getting plenty. also, babies are experts at letting you know they need more to eat.
as a side note... good luck with going back to work, it is hard for everyone... be kind to yourself, everyone will survive just fine.
oh and btw... making babyfood is fun and easy! try wholesomebabyfood.com to get you started... you don't need a lot of equipment (though a food processor is awfully nice to have). I froze mine using ice cube trays and stored it in ziploc bags.