I purchased a house built in 1960 and like other people have mentioned the terrible bounce, I got the same exact situation.
I'm thinking of installing blocking to strengthen the floor. The 7 joists are spaced 14½ However, since they're all buckled at the lower part of the joist, ranging from 14⅛ - 14⅞ I wanted to know if it's safe to wedge between 14½ blocks forcing them to move back that extra space. (see below picture)
I also so wanted to know if this load sharing would cause to much weight on other parts of floor beams.