I would suggest that cost of living is a relative term, with inflation being set against your income growth. If not, the cost of living is practically always increasing, and the term loses meaning as a result.
Given that wages, benefits and pensions are now increasing in annual terms at a rate above inflation, then I don’t think it’s unreasonable to claim that the cost of living is declining or improving, even though it’s technically incorrect to say that. Apart from in January of course, when the CPI nearly always declines.