Breast milk and formula ??

I currently breast feed and pump. The first 2-4 weeks I had an oversupply of milk and made my production decrease I accidently decreased it too much that now I can't produce enough to have saved milk. I got told to do formula and breast milk I just want to breastfeed and pump its so healthy and I don't trust formula . He started formula last night and it made him sleep way longer . He normally feeds every hour on the breast. And with breast milk he drinks 6-8 oz in a bottle so far he's only been taking 3-4 oz of formula. I've been doing formula then breast milk. I'm just doing this until I can get my supply up and enough saved milk. This is my first kid and no one in my family breast fed. Any tips or suggestions will really help . Anything to increase my supply please let me know:) he's currently almost 3 months 0ld and weighs 9 lbs 7 oz 21 inches