This is what I'm using now, but she's getting heavy... she still fits, but the bottom of the carrier sags terribly... lol. I got this online; there are many types available, even a backpack (astronaut bag).

It zips up all around, ships flat to you

How it looks inside, with her checking it out - quite spacious
I took these shots when I first got it; she was about 2 months old
I put a towel, doubled-up inside so she's quite comfy when she goes out in it