We use the tommee tippee mug -- the one that comes in a set of 4 colours with a little fold down "spout". I've tried other things since, but DS definitely likes that one best.
As for going from breast to cup, I would recommend trying this (based on our experience of easily transitioning from breast to bottle):
get DH to give the first feed (so she can't smell the BM on you)
Ask DH to strip to the waist (skin to skin contact)
Warm the spout on the bottle a little bit
Start with the second feed of the day so that she's not ravenous and you are not too stressed...
Lots and lots of (((((hugs))))