Help with nipple size for bottles for 12 day old

FTM with a lot of stress and anxiety.

My 12 day old is 5 lb and 7 oz and tiny. She is unable to latch on the breast for long and get her feed. So we are giving her the bottle.

We were initially using the 0 ( slow flow ) nipple but she had a NICU visit where the nurses mentioned that she was pulling too hard and her oxygen was tanking. So they upgraded her to 1 nipple size ( regular flow ). Her feeds doubled very well and she already gained her birth weight.

But after coming back home, while using that size 1 nipple both for my husband and I there is a lot of spillage and she coughed up about 2-3 times. This scared me.

So we got the T ( transitional nipple ) in the Dr Brown bottles. But I am worried that she is used to the higher flow that now she is not taking her full feed but she has to work for it.

What to do?