Just being honest and giving them 2-3 weeks of notice is probably enough. You could also ask about going part-time for a little while, that may turn out to be

Just being honest and giving them 2-3 weeks of notice is probably enough. You could also ask about going part-time for a little while, that may turn out to be a win for everyone - you still have a bit more income, and they can take longer to transition your knowledge and workload to someone new.