Lots of material on here regarding replacing with a metal hatch, if that's a direction you're interested in going.
Otherwise, I opted for a Tempress cam access hatch. I specifically wanted one where the hatch itself covered the whole frame, so that water would be more likely to run off onto the deck and out the scuppers rather than leak through the seam into the bilge. The cam lock really seems to seal the hatch down securely, and the hatch is sturdy with no flex at all when I stand on it. The only downside is that the cam latches themselves tend to accumulate dirt in the handles. Not a big deal and it doesn't affect the operation, but it bugs me a little bit.
https://tempress.com/store/Access-Cam-Boat-Hatches-Multiple-Sizes-p97937196