Jet 2 will not go for any s/hand 767's - Had they wished to do so before now when they had a large 757 fleet then they would have got them - Flight deck common rating.
It's all about costs now - Fuel being the biggest cost, and maintenance, the 767 is not as economical anymore - they are old and will need plenty of TLC.
The likes of United, AC, AC Rouge, and AA with large (but reducing) fleets for now are still plodding the Atlantic have made them $$$$ as the air frames have been paid for times over and they have huge technical back up.
Jet 2 have tested the Wide Body acquisition and operations by leasing A330's (reducing the £££ risk) and using them only seasonally on peak routes like PMI and TFS.
When a large aircraft goes Tech/AOG and the airline only has one or two of these aircraft then the logistics of delay recovery etc is formidable and can break an airline if it suffers too many of these delays.
I think Jet 2 has been wisely cautious.
The 737-900 is a people mover (like the 757-300) and trades performance for extra payload - not sure if Jet 2 would ever consider these -
I doubt they could operate full in and out of LBA for instance...