Nuk bottles?

My son's at the stage where he's taking 8 oz but he loves the mam bottles but it's getting hard to squeeze in 4 scoops as well as miralax as requested by Dr. Plus no room to shake. We have tried 11 oz Avent bottles and convert the nipples as well as the wide neck Dr Brown bottles but we're dealing with nipple collapsing and he's on the fastest flow. I feel as we didn't have problems with nipple collapsing when in the actual mam anti colic bottle since the air flow on the bottom but now we're having issues. Have you ladies had any success with converting to nuk from mam? Is kind of the same I feel nipple wise.