Childrens' bike if I want to put my feet down? I am a very short adult (61 inches; 155cm), who has not been able to get the hang of sliding off the seat and back on at stops (especially on hills). I really just want to be able to stop and touch the ground with the balls of both feet, but I do understand that on a regular bike, you can't do this and have the seat at the right height for pedaling.

Could I solve this situation by buying a children's bike, and then adjusting the seat up really high? It seems like with smaller wheels (maybe 24"), the part the pedals mount to at the center should be closer to the ground, so there will be less of a difference between "leg distance touching ground" and "leg distance at bottom of pedaling". Could this solution work?

Also, are there other solutions in the a-broke-student-could-buy-this-on-Craigslist price range that I should consider? (Something with gear shifting, my commute involves a big hill.)
The seat-to-bottom bracket height is important for comfortable riding and efficient power transfer.

The seat-above-road height is what you're trying to minimise in your question.  This means a lower bottom bracket, which means an increased risk of pedals hitting the ground.

The size of the wheels is utterly irrelevant to the bb-road distance.



Instead of sliding forward and standing over the bike's top tube, consider attempting to lean the bike and put a foot to the road and the other ready to take-off.



Leftmost police cyclist here is leaning to her right, the other is leaning left.  Both are seated on their saddles with one leg ready for the first power stroke.  I'd suspect female police rider is left-handed.



From left to right: Purple bag is leaning left, but has a foot on the curb/kerb.  Jeans Man is leaning left.  Can't see Red Jacket too well.  Red Bag Folder is track-standing (staying on bike without rolling)  NoHelmet appears to be drifting slowly forward while being off the saddle (prepared for a big power push when the light changes.  Other Folder seems to be right foot down.

My point is, none of these riders are standing over their top tubes with both feet on the ground.    Its really hard to find a picture of anyone even doing it that way.

Generally speaking that is only done when fully relaxed with no need to get up and ride again immediately so you'd rarely see it in traffic.



Another option if something is available.

Amusing video about how to stand with your bike: