James,
Since the Visa Waiver allows a maximum stay of up to 90 days, your best bet would be a
B-2 Visa which could potentially allow you to stay for up to a year at a time, although you'd need to show that you have no intent to attempt to migrate. This can be demonstrated by having property and a job in the UK - although I'm guessing from your post that you'll not be employed by anyone in the UK whilst you are in the US which may make things harder. Also you will
not be allowed to seek employment whilst over here and any attempt to do so (including 'cash-in-hand' or 'under-the table' type of work) could potentially lead to both deportation and a permanent ban from re-entry.
However the B-2 does not guarantee that you'll be able to enter the US on each and every visit - port officials always have the right to deny you access if they think you're staying too long in their opinion or that your intentions are not true.