Because of depositor insurance and pension fund insurance, risks are not treated as real risks. People know their lack of consideration of risk will be bailed out.
Make two kinds of banks. One very simple and safe with no incentives for risk taking. Another that is unregulated and you are risking your money. Those who don't want to deal with risk can put their money in the former and earn a safe return.
And that could be achieved by limiting a bank to writing mortgages, only loaning the first 60% of the 5-year moving average of a house's price. Require 20% down and let higher risk lender's lend the rest. Such a bank should also get paid back first.
This safe bank would not resell its mortgages and managers would never earn bonuses for a higher rate of return. Don't even offer checking accounts, just savings accounts. Don't have branches.
Keep the books completely open to the depositors 24/7.