I will add that I-81 has one of the highest accident rate in the country, mostly because traffic is so heavy and it is only two lanes each way. I’d recommend I-64 for that reason alone. The toll road is only between Charleston and Beckley and cost isn’t very high.
If you exit I-64 at US-60 Buena Vista, you’ll be on I-81 only a mile. Turn right on 501 at the light in Buena Vista, then stay straight on VA 130 when 501 crosses the river and you’ll have only a couple miles of twisty road. 501/130, though only two lane, isn’t bad. 501 from the river crossing 18 miles into Lynchburg is horrible, a true sports car road. We lose a semi over the edge from time to time. There’s a curve there with a pile of big trucks at the bottom because they can’t pull the wreckage up, no room for the big tow truck needed to lift them up.
We take the 501/130/I-64 route frequently to visit family. Have a great trip.