Your damage does not change regardless of what you have equipped. The only difference is the stats on the weapon(+stam, agil, strength, armor etc...).
Every time you level your hit skill in feral form is at the max for that level, I.E. you normally gain weapon skill points by using a weapon to kill things during that level. In feral form you are already at the max skill for that particular level. So you don't have to worry about keeping up your skill on anything from stave, maces, daggers, etc.... When you pop into caster form to hit things you will not be very efficient unless you keep your skill rating up, but you aren't going to hit very hard either way because druid mechanics are built for you to use feral forms for melee.
When you get up higher you may melee some in Moonkin form for mana regen but it's more for that than to do any actual damage with a weapon.
All you have to do is make sure you can equip everything you can so you can get the best stat set on whichever weapon happens to have the things you are looking for at that time.