You won't bend the K frame. Make sure your jack has a "tit" on the lift pad, rotate it straight back so that it "hooks" on the rear of the K. As the car goes up, the K will be tilted some, and will try and "walk" off the jack in some cases, but if the jack pad is "hooked" at the rear edge, it cannot do that
Not knowing the construction of your jack, hard to compare. I'm not sure I would recomment wood on your jack stands. Seems to me this could create a dangerous slippage situation. If you are concerned about scratching the painted bottom? Then find some rubber or even heavy rags to wrap the tops of your stands.