Do NOT take a taxi as it can take twice as long and 4 times the price depending on the time of day. Just take the AIRTRAIN to Jamaica and take the E train into Manhattan for a total price of $7.25 and about one hour of time. Yes, there is a little walking in the terminals, both at JFK and at Jamaica, but nothing too far and no stairs. Depending on where you are going, many E-train stops in Midtown, such as 53rd-Lexington Ave have escalators, so it is not a problem with simple luggage.
TAXI=NO WAY.. SUBWAY Fastest way into City