bottles?

I pump and supplement due to slow flow & low supply, and since day 1 ive been using dr browns bottles, and i love them but shes 2 months now and it takes her like an hr to finish her 4-5 ounces, so i tried an avent bottle I had and it was like feeding her out of a cup, she wasnt swallowing fast enough and it was just going all over her..  I want to get her used to "big girl bottles" so she can drink faster bc it literally takes forever me and my husband usually take turns bc it takes so long,should I just get a different nipple size for the dr browns? Or a diff bottle? Any suggestions?.. She doesnt have digesting issues or reflux or anything like that so a faster flow would be fine just dont want it to be too much of adifference