I have an old but adequate jig/sabre saw that I don't seem to be able to find blades for. I know there are T-shank and U-shank blades and my saw seems to use the latter but the blades I've been able to find recently have a shank so narrow that after a few inches of cutting, the blade angles back so that the tip trails the part fixed in the saw. It seems I need a wider shank but I can't find them. Or any kind of useful comparison between types of blades for this type of saw.
I believe you'll find that the split pin at the top of the blade holder is meant to engage a slot in the top of the blade, keeping it from pivoting on the attachment screw.
That type of blade looks like this:
You'd need to measure it carefully or test fit it to make sure it will work for you. Measuring might be easier given the package at a store is likely to be sealed.