Im in the same boat, going to Gran Canaria on the Tuesday flight which is being operated by the Titan 757. We booked rows 8 and 9 which on the 737 is just forward of the 2nd door. Having looked on the Titan website for the 757 layout its showing we now have the extra legroom seats (row 8) and the one behind. Ive had no comms of Jet2 saying we cant have those seats so I guess we will have to wait and see what happens!!