D'agh. That's a tough one. In the ideal world, Atium + Zinc, that way, if one is fully awake they've got the Atium to carry them out of danger, and otherwise the Zinc feruchemy means they're never really half-asleep. However, I don't think Atium is going to exist until Harmonium stops being the way to create nukes, so my favourite combo that would work is a Coinshot Skimmer, which I name the Astronaut, for these reasons:
1. When the Astronaut is storing up their weight, they will weigh less. However, their muscle strength doesn't decrease as far as I know, so they'll be able to jump much further than they had before, and since there is no hardcapped limit on the amount they can store, they could very easily become an almost superhuman jumper, and without the fall damage.
2. Most of the planets in the Cosmere seem to have a metallic core, like the factual universe's. So, it would be extremely easy for them to reduce their weight to say, five kilograms, then Push on the planet's core, or at least a large plate of metal embedded in the ground, or similar to that. Or otherwise if the physics doesn't work out they could massively increase their weight ("there isn't an upper limit of how much they are able to tap at any given time" according to the Coppermind article for Feruchemy) then Push, although the small matter of keeping their skeletal system intact is raised...
Regardless, I'm a big fan of using Steel Allomancy to initiate space travel.