From Jet2 website:
You are allowed one small piece of hand baggage weighing no more than 10kg and dimensions not in excess of 56x45x25cm, including wheels and handles
Subject to availability and at Jet2.com's discretion you may check-in excess baggage, on payment of the relevant charge at the departure airport. This charge is currently 12GBP / 16EUR / 20CHF / 400CZK / 70PLN per kilo.
Payment is generally accepted in local currency cash or by payment card which support foreign currency transactions. If you are planning to travel with excess baggage please allow extra time to complete the check-in process. No single item of baggage may weigh more than 32kgs.
The baggage allowance is 22kgs for each travelling customer per bag booked and paid for (excluding infants). When pre-booking additional bags in advance of travel, the allowance increases by 22kgs per extra bag booked up to a maximum of 3 bags, or 66kgs, per travelling customer. No single item of baggage can weigh more than 32kgs.