I've had some curly negs that were just too frustrating to deal with at an enlarger.... and didn't uncurl no matter what potion I tried. My attempts included packing them tightly in a bookshelf for months or pressing them extensively in a dry mount press! The thing is, these pressing methods risk damaging a neg, so it's really a last resort.
There are two non-damaging options that will yield excellent results and provide you an easily printable, flat neg to work with:
(1) dupe the neg. Put it emulsion down on a piece of sheet film, e.g. ilford ortho plus, put a piece of good glass over it and dupe it. Dupe it to thick sheet film and be happy. There is a slight risk of damage to the original due to particles on the glass that holds it flat, but you can inspect the glass very carefully, work in a dust-free environment, and in any case the contact is made on the back side of the neg. N.b. this is lensless duping so you are losing very little info and any minor scatter from the glass will very likely be far out of focus. Especially if you use thickish glass, then the top surface can even be scratched and it won't matter. So really there's only one surface to obsess over.
(2) have the neg drum scanned and get an LVT made from it. This is more pricey but you can get res up beyond 3000 dpi so it's excellent resolution that will only barely compromise enlargeability of your neg. And arguably, this method can get more real info out of the neg than optical duping becase the drum is holding the film superflat and the information is being gathered confocally, i.e. without lens abberations coming into effect. I wouldn't argue that it's better than getting a 1st generation print striaght from the original, but it's very, very close. Another thing is that you can have the dupe LVT'd to a larger size so if you want to contact print or have a smaller enlargement factor at your enlarger...
(and I'd like to take this opportunity to pre-emptively reject any assertions that drum+LVT is digital cheating! LVT has been around for a very long time and is a very powerful tool providing extremely high fidelity)