I use baby bottles all of the time and drink most everything from them. I always have at least 3 filled with warm baby formula each day. One during my night diapering, one to take to bed and one with my breakfast in the morning.
I have never had much luck making a hole in the adult sized NUK nipples so mostly used the Large size 3 baby nipples. That is until I tried the baby-pants.com silicone nipple. Before I actually used it I thought is was a pretty weird shape but once I put one into my mouth, oh my! They are heavenly! If you want to relax this is it. It hits the back of the mouth just right. The flow is good but not to fast.
My only wish would be to be able to purchase just the nipple and not the bottle. I have several dozen baby bottles and they are plenty.
I recommend you give one a try.