Mixing formula and boob milk? advice?

So i breastfed my last baby for 14 months but she was fussy, never slept and was really skinny until i introduced solids. I honestly think she was hungry... when i would pump, id get next to nothing out of both breasts. She has wet and poopy nappies but they were never really drenched or soiled a lot... i just think i had a supply issue or there was something wrong with my milk. She would go for the foremilk and wasnt drinking the hindmilk and all her poops were green. A LC said green poop = no hindmilk. So i guess im just wondering if i can get some tips for this time round? Should i supplement with formula? Do you mix the formula and breastmilk together? is there ANYTHING i can do to increase my supply and is there anything i can do to ensure baby gets the fatty milk? I dont know if its relevant either but i NEVER leaked and at 28 weeks pregnant, still dont have colostrum. I was getting about 1oz out of both breasts when pumping