which bottle??

my 7 week old is currently taking evenflo wide neck nipple in slow flow. she takes 4 Oz of similac for spit up has added rice. it's taking her 30 to 45 mins to eat and often falls asleep so it may take an hour for her to take a bottle. I tried the medium flow she would finish in 15 min with me stopping to burp 3 or 4 times, but she got extremely bad tummy ache and spit up a lot with each feeding so that flow is too much right now! I'm wanting to try a different bottle to see if this helps with her eating a bit faster but won't hurt her tummy. any suggestions?