the new 300 seat B787-8 config was a compromise so as all of the TUI airlines have the same number of seats on the B788. TOM was on the only one with less than 300 seats (the other two had more than 300).
Currently there are only 4x B787-9 which have been ordered, they're only for TOM and will be delivered one per year 16/17/18/19. They will seat 345 pax.