"Small plant" and passiflora aren't usually spoken of in the same sentence. Your best bet would be to go with a member of the decaloba subsection--I've heard that citrina and coreacea can do well as houseplants. Be aware that even these need a good deal of light to flourish.

I have biflora, Um... Capsularis, sanguolenta, herbertiana... Um...(been a long week) and several others I cannot remember at the moment all growing happily together in one 12" pot. It sits in the (big) kitchen window thus gets a good blast of sun every day. As they grow I just keep wrapping them 'round each other.. So I kind of have a 'plant ball' with no idea which is which until they bloom.

All of those are "small" tho, for passiflora. Or at least they bloom at a smallish size.

Quinquangularis is another, as is membranacea.. but that particular one's a lil spendy for a beginner.

Here they are:

{{gwi:1133713}}

7 or 8 plants in 1 12" pot.