Lump sum amount enough for what you calculate for your son’s enrichment from his part would be fair enough.
I would advise you to not to carry the psychological baggage of his financial assistance apart from the son’s responsibility of his, as you are an independent and decently earning person. Be independent and self capable as you are. That’s the highest ground what one can have for themselves.
And start afresh, with wisdom and thorough understanding of whatever you find best to carry on forward.