Buy utility preferreds. Average yield about 6%. Whenever one appreciates (say about 40 cts which is approximately the amount of a quarterly dividend), sell it and replace it with one with a higher yield/lower price. That way you'll bump the yield up a bit by taking periodic capital gains. Most are currently trading above issue price ($25) so you'll have to be cognizant of interest rate hikes.
These days, what is risk free? Us gov't paper? Easy to argue that isn't risk free. Debt to gdp etc... But to give my 2 cents... I would say individual corporate bonds with names I feel safe in. But for ease perhaps csj. The ishares short term investment grade bond fund.
It can be more than a year. For the listed suggestions, how does the additional risk scale with the additional profit? Is it a linear relationship?