Can you get him a mattress that's big enough for both of you - that way you go to him and can perhaps have a snooze too?
And try your darndest to wear him our physically during the day - the more he runs/climbs/dances/swims the better he is likely to sleep.

I think it is OK to tell him during the day that "when you are quiet during the night Mummy gets more sleep and we can have more fun tomorrow" - I don't think of that as "conditional", more just helping him see the connection.