Another option might be Monroe Sensa-Trac coil-overs. I had them on my Safari. It fixed my sagging steel leaf problem, although it rode a little harsh unloaded. They were great when towing and hauling, though.
These would fit your Suburban...
Hardly anyone swaps their box for a flat deck here (except fleets). I always thought that would be a great setup for a lot of guys around here. But no, people would rather carry their two quads or skidoos up on those stupid elevated aluminum platforms.
OP, I have the same truck ('16). Do you...
Or you could run up to Lowe's in Prince George:
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How about something like this?
Flat Deck Trailer 16 ft. $900,