Generally speaking, English once used 'you' as the second person plural (equivalent to 'vous' and 'vós') and 'thou' as the second person singular (equivalent to 'tu'). When talking to a person in a higher position, one would use the polite 'you' rather than the informal 'thou'. Nevertheless, as time went by, the polite 'you' (nearly) erased 'thou' from existence and became a simple form of treatment without distinction between formal and informal.
I'm attempting to translate a historical novel set in medieval times. The use of the formal/polite 'vous'/'vós' often gives subtle but important cues for the plot, therefore I decided the simplest way of maintaining these cues would be to use 'thou' and 'you'.
Technically speaking, 'thou'='tu' and 'you'='vous'/'vós'. However, usage has caused modern speakers (I believe) to see 'thou' as more formal than 'you'.
Should I then translate 'vous'/'vós' as 'thou' and 'tu' as 'you'? And would that suffice to transmit to the English readers the aforementioned cues?