B.,
When I breastfed my daughter well-minded friends told me that I would confuse Chelsey if I switched from breast to bottle. But if done correctly none of that will happen. :-) In my case it was a necessity. :-)) But when it is time for your little one to drink or if you notice that he is wanting one,then bring out the sippie cup. But since he is still young don't fill it up all the way. If it is too heavy, it may discourage him from using it.
When I started Chelsey with her's, I would pretend to drink from it. She then would want it because she thought it was something that Mommy liked. Needless to say I had to try several baby foods in my time. :-)) But so many new brands have come out since Chelsey used hers I couldn't tell you.
But I can tell you let your baby be a part of the selection. First find a brand that you like then let the little one pick out the color. Chelsey had one that she like the most and as long as I was able to watch over it, I would let her have it (It was a gift from a family member). But it seemed to be the color that she like the best. The one I bought seemed to be only used on car rides and when we were visiting. Otherwise, she didn't want it.
So first, find a brand that you like and takes care of your needs. Then let the baby have some fun too and pick the color or something (a character or design) that will actually help to make the conversion more pleasurable for both of you. :-)