scruffymax, if you try a straw my recommendation is to buy some straws, cut them in half/shorter if necessary and use with a regular cup or one of your bottles without the teat on. I say this because I spent out a fair amount of various straw cups only to find that I couldn't truly get the milk out of the straw when washing. I would prefer washable to disposable but disposable seems cleaner.
If you don't like waste you can wash the straw and pop it in a craft box for counting, colour sorting, making pictures, sticking in play doh, threading with cotton reels etc so they get used again.