SUPER easy: https://www.uscis.gov/working-united-states/temporary-worker... You do not need a lawyer and the letter of employment can be done by the HR department of your employer, just be sure to include everything they ask for. I did it all by myself and got my company to reimburse me the fee after I came in to work.

For sure sell yourself with a TN Visa, there's NO sponsorship required, just disclose the fee payment. I'm a Mexican who did the whole process by myself, no lawyers from the company required, and even though it's easier for Canadians since you just go to the border with the requirements and pay a super small fee, you get right in and can start working the next day after you come into the states. Assuming your profession is in the TN NAFTA list, you can get to work within a week with a TN Visa.

Hey Peter, I'm about to expire my 60 days of grace period for finding another employer under TN visa, has the USCIS said anything about extending that grace period because of coronavirus? Also, if my visa is still valid until September, can I just go to an airport POE and change my employer there with a letter of employment? Thanks!

Responses in order: No, USCIS has not yet extended this grace period or relaxed expiration/departure dates but it might. There's no change of employer; this would be a new TN application with your new employer. But of course there are travel restrictions in place now that could impact your departure from and return to the US.