u/No-Caterpillar-2426

I am replacing tub due to cracking and when I pulled the tub I noticed the subfloor beneath had damage and needed to be replaced. I cut out the subfloor and I am trying to figure out how to properly support the new subfloor, specifically around the edges.

On the sides, the joists are about 5 inches back underneath the tile and wall. I am not replacing the tile. I dont think I could scab or sister them to have a proper lip. No access beneath the bathroom. Is it okay to just add blocking around the edge between the joists to add strength and prevent sag? See pic of general idea.