The details: The house is 4 years old. The floor in question has a 16 foot span and the floor joists are 2x10's on 12 inch centers. OSB subfloor, I don't know how thick. There is cross bracing, but I suspect not enough as there is only one set of cross bracing approximately in the middle of the span.
I have access to the entire underside from the basement so can do pretty much anything except add a support column (I want to use the open floor space below for a pool table). I am planning to have the basement area under this section finished and expect to do that in a couple months so I want to make sure I address the floor bounce issue once and forever before that work is done.
Some options that are being considered:
(1) Additional cross bracing or perhaps solid blocking at 4 foot intervals.
(2) Rip 3/4" plywood to width of joist and sandwich on each side of joists to add stiffness to the joists, maybe only in the middle of the span.
(3) Glue and screw 3/4" plywood sheets to the bottom of the joists in the center of the span (i.e. a subfloor on the bottom of the joists).
The last one was suggested by my brother-in-law. He sometimes does things in a bit unconventional way but he always seems to get good results. Contractor I talked to said he'd never seen it done but was "worth a try".
So, any experiences or advice on solving this? My objective is to get the best result I can, I don't mind spending some extra time and/or money on it to get the best results but don't want to waste my time on something that will have no impact.