You can jack on the frame. It's best if you can spread the load out. And, as you said, you'll need a fair amount of cribbing to get the jack high enough.
If it's a torsion axle, you jack where the axle is mounted to the frame. There's usually a square tube there that you can get the jack under.
Otherwise, I don't have torsion axles and will jack between the u-bolts, on it, or very near it. Like so:
Otherwise, lots of people use a ramp like the
Trailer Aid. While others have concerns about you overloading the tire that all of the weight is then carried by.
Hope that helps!