I use a 12t shorty hyd bottle jack that has a 10" X 10" base made for side of the road use.. It has a U channel adapter on top made for jacking from the axle tubes.
Axles tubes on a std leaf spring suspension are not soft and placing a jack under one next to the U bolt will not bend or crush the tube.
Jacking from one end of a 3500 lb axle is lifting about 1500-1800 lbs at the most.....not the whole side of the trailer.
The reason axle makers warn against jacking from the axles is some try jacking from the tubes to far away from the U bolts and of course will bend the axle creating more camber bow.
If you use a product like the clicky or make your own make a dry run at home. Many found out the hard way on the side of the road the device didn't lift the flat tire off the ground.