I would suggest a step beyond though, because rebalancing your portfolio is fun year 1-5, but not so fun year 5-20: have a look at e.g. Vanguard retirement target funds.
Essentially, it's an ETF with a rebalancing rule included for a specific target date. For instance if you buy the target 2050 (your hypothetical retirement age), the ETF rebalances itself between bonds/monetary fund/stocks until it reaches that date, u til it's pretty much all cash in 2050.
Lowest hassle diversified retirement scheme I found.