How to plan to live on a reduced pension?

The earliest my employer allows me to receive a 50% pension at 55. If I wait until 67, my max pension is 70%. My employer also offers retiree healthcare "at much lower cost than the private insurance market" for pension recipients.

How can I plan to take the pension at 55? 457, taxable brokerage, Roth IRA? or a combination of all three?