Look on line for what to do besides the museums, monuments at "Washingtonian" and "Time-Out".
You'll find the new exhibits reviewed as well as restaurants and shopping.
Staying near the Mall is an idea I agree with as it keeps you nearby. We stay at the Hay-Adams for that reason.
Remember that almost all the museums in DC are free so take the 15 bucks p/p you would have used and treat yourselves well in other ways- dining, souvenirs, etc.
Ask your hotel's concierge or front desk to reserve tickets for the new African American History Museum in advance of your stay should you have an interest. Entrance is free but you still need a ticket.
See if there is a WF near your hotel; reasonably priced buffets for breakfast, lunch, or dinner.
Old Ebbit's has a happy hour most days of the week with prices lowered on oysters and seafood platters. They also do takeout (but no delivery) if you are too tired to go out after a long days sightseeing.
Be sure not to miss the various historic homes and estates in and near DC:
https://www.smithsonianmag.com/travel/summer-visit-dcs-coolest-beaten-path-estates-180955928/?page=2
Years ago, I bought a Michelin guide to DC and it's been useful in making an itinerary for visits. My copy is out of date when it comes to travel routes and such ( it's almost 30 years old) but the building locations haven't changed

.
Use public transport as much as possible. Much like NYC, DC is not car friendly.
Have fun. We go about once a year and I
still haven't seen the Jefferson Monument and finally made it to the Lincoln last year, LOL. Too much to do makes this city a delight.