In my strong opinion an investor should seek to invest in assets where they are able to identify opportunity.
In this case, rather than identifying singular opportunities, the OP is seeking to invest in
all opportunities by holding index funds. It seems pretty clear to me that the OP isn't at a point where he either wants or has the ability to invest in individual assets, and would rather hold low-cost funds for both the simplicity and reasonable returns. There's no shame in that -- it's an approach that is known to work
pretty well, particularly for people with limited investing knowledge or with limited desire to "dissect" stocks (as advocated by
Graham).
My interpretation of the OP's post is largely that he doesn't want the most conservative strategy, but doesn't want the most aggressive one either, and I get the feeling that he is ready to invest for the long haul (given that he stated that he's seeking a long-term strategy). As a result, the OP may find the following
link relevant to help them put together a portfolio.