Rear shock replacement (2011 Sequoia Platinum) with adjustable ride & air leveling?

2011 Sequoia Platinum with auto level and adjustable ride.

I've searched high and low. Cannot come up with an aftermarket solution to replace my leaking rear shocks. Factory replacements are $700+ each.

Been leaking for a while. Recently purchased a 5500lb (wet/loaded) travel trailer and use WDH from day one. I have not experienced bottoming out. However...recently with the shocks worn, I sense more "porpoising" than usual. In short, I think the towing accelerated the wear of the shocks. I would like to find a more robust solution.

Any ideas where to source shocks?

Should I plan to add airbags with the towing setup described above? It doesn't sag currently.

Thank you!