I need to replace a 35 year old toilet. Am thinking of buying a Kohler
Highline from Home Depot. Toilet would need to be elongated, gravity
type and ADA compliant. Toilet would have to deal with bulky stool
which floats. Old toilet can deal with urine but not with floating
solid waste. Is the Highline a good choice? If not can anyone
recommend
a good choice?

I installed a Kohler in 2002 and a Am Standard in 2005. Both work well,
but I'd give the AS a slight edge. It seems to have more "oomph" on the
flush.

But you won't go wrong on either. The Kohler uses a tripod
configuration to mount the tank on the bowl, and that makes it much
easier to level it up.