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You could use OmniFocus to remind you each month to add the various bills to the spreadsheet showing the running tally.

As for the concern about accidentally checking off an action, for this sort of thing I make notes in the note field ("11/11 received 30 quid from Alan for Oct. utilities") and when I do my review of that project (you are using the review feature, right?) I make sure anything marked complete has the necessary supporting details to justify being marked complete.