Ideally when you are getting up (from either side) you don't need your arms at all.
When sitting (front side downhill) pull your heel side edge as close as possible to your butt (more knee bend, how close are your calves to your thighs?) Dig the edge in hard as if you were carving. Lean your chest forward between your legs, including arms downhill of the board, so you center of gravity is close to over the board. Now stand UP with your legs. It's actually about flexibility more than strength. Your legs will be plenty strong if you have the starting position right.
You can practice this by sitting on the floor at home (no board, boots, snow pants, perfectly level floor) and just stand up without using your hands.
One nice thing about this way of standing up - if you slip you fall on your butt again instead of jamming your hand / wrist / arm.
The reason it seems harder to get up on heel rather than toe edge is the center of gravity tends to stay over the board when using toe edge.
The reason why most beginners have trouble is their calves are weak (you may think they are strong, they are not)
The most serious problem for most beginners is not knowing how to fall down properly. Roll on your shoulders or belly flop. Do not jam arms out front or behind you. Your wrists will thank me.
The reason why beginners fall down a lot is a combination of two factors: 1) they go to slow making it harder to turn and 2) they fail to look where they want to go. Looking down at the snow, at trees or at other people usually results in some type of wreck.
When sitting (front side downhill) pull your heel side edge as close as possible to your butt (more knee bend, how close are your calves to your thighs?) Dig the edge in hard as if you were carving. Lean your chest forward between your legs, including arms downhill of the board, so you center of gravity is close to over the board. Now stand UP with your legs. It's actually about flexibility more than strength. Your legs will be plenty strong if you have the starting position right.
You can practice this by sitting on the floor at home (no board, boots, snow pants, perfectly level floor) and just stand up without using your hands.
One nice thing about this way of standing up - if you slip you fall on your butt again instead of jamming your hand / wrist / arm.