I have been in business aviation for 6 years, and now in the same orange loco as you, also close to be upgraded.
Very simple: DO NOT DO IT, the grass in not always greener on the other side. Easyjet, especially if based in France, Italy or Germany, is one hell of an employer, and you would be mad to give up an upgrade there. Aside from KLM, Air France and LH you probably have one of the best gigs available in Europe, money and overall conditions wise.