Most standard MX keycap sets should fit the QFR - there are no surprises, standard spacebar, standard 1.25x modifiers etc.
The only two possible problems are the caps lock and scroll lock have LEDs under them, but you should still be able to see the lights with most keycaps.
The second is that the pins under the keycaps with stabilisers can be very difficult to get out (mine were, I nearly lost two fingernails in the process).