I used to keep a large compost pile. I would amend with that every year in the spring. Each plant gets a handfull of pellatized gypsum, potash(if needed), blood and bone meal. not a lot. dust the bottom of the hole. fill with a thin layer of dirt. set in your transplant, then fill with dirt halfway and dust again then finish filling. water in deep. I always get great results with my tomatoes . the root systems i pull up from some of the plants stretch for feet outwards.
I had to start new beds and Ive always built my own soil. I mix peat moss, pro mix, composted manure, mushroom compost, vermiculite, and perlite. I couldnt tell you the ratio. I kinda just add and mix until it feels right.