Rectangular, box-shaped drawstring bags are standard. Lately people have been making the bottoms roomier than the tops so that people can put little items in with the deck--like herb sachets, for example. Several sites sell bags. You could give them a look-over and use their samples as a departure point.
I like making circular drawstring bags because they're a little bit more of a challenge. They present different design possibilities which may well make them more desirable.
Those bags with a wrist strap from baba seemed to go over well. I think they had zippers.
I can't give you an opinion about "purse" type bags. I wouldn't use them, personally, because I'm carrying around too much stuff with shoulder straps already--purse, recycle bags, small bag for files, etc. etc. I like my tarot to fit into something else. However, I can see the appeal for someone less burdened than I.
Couldn't hurt to float a few that were sort of neutral, outwardly--not specifically tarot. That way they could sell for purses if no one wanted them for tarot.
Good luck with your venture.