The most stable base I've come across is still the Bohemian crystal vase
but it will not fit a KM or Temsaah despite being size 26 due to the lower part of the neck opening and height. They are heavy due to the leaded glass, pyramid shape, but expensive and although some are still for sale, they aren't really being brought over anymore.
The next most stable ones I have are some Syrian trumpet vases but those are quite tall and hard to find also. After that would a tie between some wide bell shaped Syrians and Bohemians that I have.