I have never seen 7/8" thick wood flooring but I guess anything's possible. Probably the easiest thing to do would be to use 3/4" thick floor and shim as needed using roofing felt.

It's an old house and many of the materials are of odd or older sizes. For example, in our house, a 2x4 measures 2x4. I was able to use a carpenter's measure and confirmed twice the wood flooring height as 7/8. Long talk with DW over a bottle of Sav Blanc and we decided to stay with the old floor and do as much as we can to clean it up and refinish.

Use luon sheets to raise it up will be better then shims. Luon is less then 1/4" or double up on rosin paper.

#30 roofing felt would work ideally. May need to adjust accordingly along with #15. Rosin paper is too thin, would become too cushioned...potential squeaks