Your first couple criteria are at odds with the final "does not take up much room". The small easy to store ones are not going to be big, rugged, and indestructible ....
The better answer is *more* reflectors at a greater distance down the road. Always treat them as if they are a single use item.( = Don't be bashful about putting them near the edge of the road ).
If you are really concerned about visibility at night, forget about the triangle gizmos. Get some sort of blinking light instead.
Another hint - don't pull over just past an obstacle or curve that puts you out of the view of approaching drivers.(unless you are a cop with a radar gun). Saw that one maybe three times today ....(the disabled vehicle part, I saw more than three cops with radar guns