Not sure if this will help much as we live in ireland but we have a through floor wessex lift. THe good thing about it is it is push button but don't need to keep finger on it to keep it going ( my daughter is only 8) and the doors electronically open and close.Also it was a renovation of our house -all that was needed was to cut through the bison slabs (we have concrete floors between ground and upper level ( a dormer bungalow). No shaft or anything and you can actually incorporate it into the floor space-as in when it is down you can walk/wheel on top of it upstairs. People often have them coming up into the bedroom. Ours is in the hall (was a storage closet).
Big downfall to a child is the speed in which it goes up/down. Takes three times the length of time to go up as it would to be carried up-hence still carrying at times but at least chair can go up lift.
It is also extremely safe-stops when anythings hits against it or anything or anyone is below when it is lowering.
Just glad she has full run of house, however if new build would go bungalow. - My parents have bungalow and she loves it-easier to be heard when calling for help and no hassle/delay going from room to room. Just a child's perspective! Enjoy the challenge!