Hi, have a look at seatguru.com. I don't know if they specifically show Thomson's seat but if you know what type of aircraft you are flying in you should be able to get a seating plan.

Hi Red

Thomson planes are 2-4-2,seats can be booked from row 7. First Choice planes 2-3-2, seats can be booked from row 15. Reserve your seats approx 4 weeks before you go at a cost of £10 per person both ways.

Hope this helps

Sue