I have been breast feeding my baby boy who is 11 days old

He was born 10lbs 6oz so was a big boy (more so in length that being chunky)

At his 5 day check he was 9lbs15oz which was within the 10% allowance for weight loss

At his 10 day check yesterday he was 9lbs 6oz but still within the 10% allowance but they were slightly concerned that he had lost further weight instead of putting it back on

For the last four nights we’ve been giving him formula because he wasn’t settling of a night time. The tub recommend 4 or 5 oz for his size but we only gave 2oz in case he got used to having larger amounts. Even off of that he settled straight away and has been sleeping for 4 hours whereas he would not sleep at all off just boob

I have started pumping and seem to get hardly any milk. I thought it may have been because I was pumping 30 minutes after feeding him like is advised so I started to pump instead of feeding to see how much I could get and I barely get half an ounce off of each boob. Only once have I managed to get 1 and 1/2oz. I have introduced another bottle of formula of an afternoon

I have decided to try and move him onto mainly formula but obviously don’t want to do it straight away and want to try and still breastfeed so he can get the benefits of it but I don’t know how is best to do it. I don’t want to give him an upset stomach and also don’t want my boobs to end up sore etc.

Should I add an extra formula feed a day over time? If so how many days should I wait before adding another formula bottle?

Or should I still offer boob and just top up after feeds?

Or is there a better way people have found to move from breast to formula?