If you put "Pet Insurance" into a search engine, you should get a whole list of companies. It does mean wading through quite a bit but it does allow you to compare premiums and exactly what cover you get for that. Some packages include cover for things like alternative treatments and if you are not into things like that, you can save money by choosing the next package down. Some policies will also lower the premium if you agree to pay a higher excess.
While some policies do say "cover for life", do check that there is not a limit on this. My boys are insured with More Than and yes, it is a cover for life policy, but I can only claim a maximum of 6000 pounds per illness and condition. Pet Plan for example, have a package where vet fees are unlimited.
One thing though - I wouldn't recommend E&L insurance. You may come across it in your search but they are notoriously difficult for setlling claims and more often than not, claims do not get honoured leaving you to foot the bill. They are nice and cheap but that is the reason!!!