Bowed floor joist

[Stevevan]

I have an older house that is 24 feet wide. The floor joist which are 12 feet have sagged in the center. The crawl space is tight but I would like to jack up the centers of the floor joist and support them with 4 x 4 or 6 x 6 post.
I am considering using adjustable jacks or blocks on the supports.

Would I need a footing under the jacks or blocks to maintain them under the house?
Will this solve my problem?

Outside and center footings are in good condition.

[pushkins]

Yes you would be best advised to add a concrete footer underneath any support system you use to level the floor, otherwise your floor will where you started from before you know it.