Lie-flat seats are usually only for the premium folks at the front of the plane, but Lufthansa is now offering an option to buy the whole row at a discount and stretch out for your flight, and give you a pillow, blanket and mattress pad.
The airline is advertising it as Sleeper Row, and is extending the plan to selected long-haul flights after a successful test on the Frankfurt-to-Sao-Paolo route. The option adds €159 to €229 over the cost of buying one seat.
On the other hand...don't count on it being there when you want it. It's only for flights over 11 hours, and it can only be purchased at the airport just before departure, because it depends on whether there are enough unsold seats. Also, there's a maximum of three Sleeper Rows per flight.