Get yourself a garden kneeler Dave
I spent a lifetime removing old nails and tacks from floorboard in my work, quite often
I furd the best way ti get them out without damaging the wood is to get a short, flat strip of metal, place it adjacent to the nail, try to grasp the head with a pair of wire cutters and lever it out using the bar as a protective base
Slow at first but until you work up a rhythm
The worst job I ever had was trying to lift floorboards that had been fixed down with wooden pegs two-hundred years earlier
Donch'a just hate clever-clogs craftsmen ?
Jim