Thank you for that comment, I just tried the hotbar method and it works, but unfortunately not for the off hand.
Example: My druid is carrying a club and a shield. I put a quarterstaff in the hotbar, click the hotbar and voila, the quarterstaff is equipped. BUT, now the hotbar only shows the icon of the club, but not the shield, so when I want to quick-change to the club shield combo, I can equip the club through the hotbar, but I have to open the inventory to equip the shield. The same happens when I drag the shield explicitly to the hotbar, the next time I equip the staff, the shield is not in the hotbar. Same applies to a secondary weapon in the off hand.
