Given your time constraints, premixed fertilizer is just fine.
Burying small amounts of kitchen waste in your garden will serve as mini composting of sorts with the only time being a minute with a trowel.
I use Vigoro 'blue crystal' stuff for pots, and compost for gardens, occasionally some commercial fertilizer. A ratio of 3-1-2 (6-2-4 etc) or close would be fine for everything. I think there's more expense in chasing specialty fertilizers.
