She is really trully just on the brink. At home we do regular undies full time, except night time she has been wearing either a bumpy or bright bots trainer. The bumpy's I actually don't care for too much because to me they seem kinda bulky and don't fit as nicely as undies under her clothes. She has a large (long) bottom. Size 4 undies fit her and she just turned 2 last week. We had the same problem fitting most diapers under her clothes. The bright bots fit much trimmer and are what we usually use when going out of the house. But it has only been a little over a week since we stopped using diapers or pull-ups out of the house. And my husband also preferred diapers if he had to watch her - but now he will have to do undies - LOL! The only accidents we have had (aside from her first day of Montessori school where she had a nap time accident) in the last week was little ones when she said she had to go potty, but either had already trickled a bit or I couldn't get her there fast enough.
My other requirement was hoping for something we could wash with regular laundry since we aren't doing diapers any more at home either.
So I decided (and the school agreed) to try a waterproof diaper cover over her other trainers (mostly gerbers and bright bots).
This is mostly for naps even though at home she never pees during a nap, but potties after. Her first day of school her only accident was nap time.