Someone who will fight for you. Decide on a number and terms you want from the company and have the attorney communicate. Last thing the company wants is the release of claims unsigned which is why they offer you a severance. A decent HR attorney is worth hiring it sounds like, especially if there are issues with unpaid profit sharing. The severance they offered you is not their best offer.

If they walked you out in a demeaning fashion, have your attorney use this also as ammo. While a lawsuit is not preferred as this might be known to future employers, have your attorney tell the company you are willing to sign the release for X, Y and Z and be willing to come down a bit from there.

Just my $.02. Recently retired and had to go through this process at different times as exec in my career.