UFH and painted floorboards

We are hoping to build old-style farmhouse and would like to have painted floorboards in some of the rooms. Is that possible with UFH (geothermal)? We understand that engineered boards are the best choice but it's hard to find unfinished engineered boards and there are too expensive to paint over! We would hope to use red deal or pine boards (painted and varnished) but are worried they would not be suitable for the UFH.
Thanks for any suggestions.