I remember reading a feat once where rolling a nat 1 made was treated as rolling a natural 20. I THINK it was fortitude saves only and that it had some heavy prereq costs.
Could have been core 3.5, third party, pathfinder. Unsure. If anyone knows what I am talking about and can help me find the source it would be much appreciated.
I believe your thinking of 2 seperate 3.5 feats. 'Steadfast Determination' allowed you to treat a one on a fortitude save as just a 1, not an automatic failure, so if your total passed the DC you would succeed while also allowing you to use your Con for Will saves instead of your Wisdom.
The other was a Luck feat called 'Dumb Luck' that allowed you to turn a natural 1 into a natural 20 so many times a day for saving throws.