Tricia -

very accurately move your plant to a bigger pot and pot it a bit deeper. use the bamboo skewer or something similar to support the stem with a couple of ties. My prefered mix for sinnigias - 1:1:1 plus a bit of milled NZ sphagnum moss and a bit of coarse perlite.

You probably have a young plant. With time the tuber will grow bigger and will produce stronger stems. But most of the time medium size sinnigias benefit from a discreet support. Most of the sinnigias that grow upright - are the ones that like full sun and are grown outside or in a greenhouse. The home grown plants are not that strong.

It is a beauty.

Irina