What about water?
You can start small amounts of water around the same time you start solids. I think I started this around 6 months with water in a sippy. They don't drink much and you don't want them to as you really want their hydration to come from BM and you don't want their bellies filling up with water instead of BM and water can mess with electrolyte balance in a mostly BF baby. For us, it was mostly a way for DD to get used to the sippy. For the first several months, she would mostly just play with it and chew on the sippy part and that was fine - her hydration was coming from BM anyway, but eventually she would take little sips as she got older. It seemed like a really natural progression that as she became more dependant on solids and less on BM, she would drink more and more water. She was heavy nurser for at least 2 years though, so never drank all that much water until she weaned at 2.5.