Soil and potting

Hello my plants are around 4 inches tall atm in plastic cups and miracle gro for soil. I didnt know miracle grow was bad till it was to late, so I was wondering where can I get some good soil to put my babies in? Also what size pots should i transplant them into?

Apparently the rule of thumb is one gallon for every foot of height.i would guess move up to one gallon containers and from there transplant to larger ones. I just start my lil ones off in 2.5 gallon pots,they spend they life in that one pot so i dont know much about transplanting. you can get other types of soil at gardening stores. it seems as though Miracle Grow has a monopoly at Home Depot and Walmart