You're a very kind Dom even to think about a bargaining situation with the sub. Normally I'd get what I was given and it wouldn't be up to me to choose. But, as you mention it, I'd probably agree to a month in chastity. Then after the month was up, if I was put in the chair again, I'd get a spoiled orgasm and a knob polishing of one day off the sentence of another month for every minute of polishing I could stand before yelling whatever word we'd agreed on.