Why not Psijamming helms?
Also Psionic Bone Runes could provide living creatures with built in propulsion, by inscribing a psijamming helm, or the propulsion method of a Stronghold Space, or any other motive effect from a psionic item into a creature.
Furthermore, psionic telekinesis works for movement in outer space, as acceleration at near distances, and psionic teleportation works for medium distances, especially if either is crafted as an at will effect, and finally Greater Teleportation works for interstellar travel, so long as you get the visualization right and don’t pop in too close to the star.
Lifeshaping could also work, but it would work even better if you include some science. Perhaps my heresy idea of ancient astronaut aliens being the source of all humanoids on Athas would fit here. That would allow us to incorporate some of the d20 future psionics and mutations as part of lifeshaping effects.
Mutations can get us non-psionic and non-magic telekinesis and teleportation.
Photovoltaic bio-crystals can convert light to electricity which can then be converted to power via energy absorption or a variant version of it. This could also provide sustenance effects as well as absorb radiation and cold damage for energy, while handily protecting one from the rigors of space. Not realistic, but that’s D&D rules for you.
If we allow science, then we can tap d20 Future for converting devices into lifeshaping.
Just some of the cuff brainstorming.