Porch is sagging, want to install new support.

Hey guys! We have a wraparound porch with a home built in 1995. The porch is missing tons of support. The wood is still in beautiful condition, everything has been protected by the roof overhang. We are in a place with pretty bad winters. I'm wondering about how to add more support. I was told to use a bottle jack to slowly prop up the porch to the right height, put either cement blocks on rocks or pylex screws, but screwing these under the deck where's there's already not enough clearance would be a nightmare.

Just to be clear, the porch isnt sagging because the wood is bad or anything like that. They didn't install enough posts and some of them are literally sitting on top of the dirt.

There is virtually no water or snow under the porch ever, if that means anything. Thanks!