You can use an open cup (no lid/spout) at any age, but it has a knack to it and takes some getting used to, you may lose some or a lot of your precious milk along the way. You could test it with a bit of cooled boiled water to see how you get on before deciding whether to go for that or bottle. Different bottles get different results as well, I would try the newborn teats first before investing in others, as baby will be new to bottles a slower flow might be useful.
I found some good advice on the kellymom and NCT websites. I think I'll just try a beaker and bottle with slow flow teat and see what happens! He has a really strong suck so my worry is anything too fast flowing may result in more air intake. I think my beaker is free flowing, not sure if I need a valve?
This may all be purely academic as I may have left it too late!