Aye Andy,
Welcome back to the forum.
From the sounds of things a XL600 would fit the bill, as might one of the MZ 660 trail bikes. As you say, the DR/XT and KLR are all in the frame, reasonably cheap, easy to maintain and run for ever providing the oil and filter are changed regular and often. See what comes up on your local Gumtree etc and ask around for other peoples trade in machines, if a dealer is having problems shifting older stock.
However, speaking to a friendly dealer, he reminded me that good secondhand bikes are in demand at the moment as you do not loose the VAT or depreciation as you role the thing through the doors onto the forecourt. Many are struggling to sell as many new stock as they have lined up in the 'recovery'!

If you are going to buy 2nd hand go hunting in the autumn as dealers want to unload trade-in stock to pay the wages over the winter months.
Trust that you are in good health. Happy hunting!
My regards, Bill.