@Dan Durusky lots of great advice already in this thread. If I were you, I'd play out a few different scenarios.
1. HELOC. If the house is a primary, consider keeping it and getting a HELOC before moving. That way you can tap into the equity in addition to some cash flow resulting from the low interest payment.
2. 1031 exchange: what would you buy as your next property? You'll want to have this planned out so that you can make the exchange occur on the correct timeline (if you go the 1031 route).
3. Selling outright: depending on how much profit you've made, this may also be an option (speak with an accountant). This could allow you to put your profit into a few different deals.
4. STR/MTR: Boston metro has tons of hospitals, could you rent to traveling nurses and get more cashflow while keeping the house for potential equity gains in the future?
I think it all comes down to personal preference on this one, but you're in a good situation!