Organic-based products is the way to go. I know some people have issues with the origination of Milorganite, but it is poop that has been processed by bacteria and then heated and pelletized. The result is a slow-release product with 4% iron (more than most other products when talking about #/sq.ft) that won't jack up your lawn. Organic-based products are activated mainly by beneficial microbes and will not burn. These same microbes will bust thatch. Golf courses, sod farms already use biosolids such as Milorganite for fertilization and some of the best kept lawns perhaps in your area. For sure, it is not exactly cheap since a bag will only cover 2,500 sq.ft., but there is nothing quite like Milorganite on the market.