We’ve found the equivalent of a Tum tum in B&M for £3 but they do need to be able to use a soft straw x
I used a tum tum 3 in 1 trainer cup for milk with my eldest and used their weighted straw cup for water. I found having two different cups for different drinks seemed to work for her.
EBF here but our son learned how to use a Tum Tum straw cup when I put BM in it, and they're pretty good at being non spill! Also no valves, just a weighted straw.