Wait a minute... Springs support the weight, that's all. The shocks control the ride. Unless your springs are dead and sagging, and your complaining that the ride is too soft, why would you go to a stiffer spring for a better ride? Unless yo want it to ride like a BMW, I would think the softer the better. Go get a set of stock, good condition FJ62 springs and a set of quality shocks, then strap on a FJ62 rear anti-sway bar, and you should be fine. What am I missing here???
Edit: you already have a FJ62 so no need to hunt down a anti-sway bar and you may just be able to take your springs in to get them reconditioned (checked for cracks, re-arc, new bushings, etc.)