Replacement Oil Boiler

Hi,
Our 25 year old oil boiler is finally on it's last legs and needs to be replaced.

Has anyone here gone through a similar process and can give advice? We live in a twenty-five year old bungolow about 1800 sq ft.
Anyone know what the best boilers are, what they cost and what the cost of fitting would be?

Any other tips or nuggets of advice would be greatly appreciated.

Thanks in advance to any replies.