I know that Sassy/Mam have a cross cut nipple intended for use with thicker liquids. The Soft Landing sells them in their online store - http://www.thesoftlanding.com/samamulni2pk2.html
I also wanted to share some information with you regarding Avent bottles. I have been nursing/pumping milk for my three month old daughter and started using Avent bottles within the last month. I selected them because I liked that they had a newborn nipple intended for nursing babies and I thought they were BPA free. After I started using them, I learned that they are NOT BPA free as I had thought. I have done lots of searches and found two sites that were very useful in helping me make a choice on a new bottle:
The Soft Landing also has an online shop that sells BPA free products – bottles, sippy cups and teethers, among other things.
BPAs are something that we need to be aware of when selecting feeding products and toys. BPAs are an additive/toxin used in molded plastic products that have been found to mimic high levels of estrogen in laboratory animals. The BPAs leech out into our babies’ milk/food when exposed to high temperatures (in the microwave and dishwasher) and over time when the plastic gets old and scratched. We don’t really know how it will affect humans, but who wants to take the chance?
I switched my bottles to Green to Grow – they have regular bottle neck and wide neck options, and they’re compatible with different nipples. The Soft Landing site did a comparison of the new BPA free brands and their wide neck nipples and found that they are pretty much interchangeable.
I know I just gave you much more information than you asked for, but I wanted to share what I learned….