[quote=@Fading Memory]
You could do any weapon you’re proficient with; I’m just making sure you’re specifically wanting a club instead of a mace or morningstar or warhammer or flail, etc.

And would you prefer the shield to be a reaction that becomes better than a normal shield long term, or the normal shield bonus? The Behemoth is a wily thing for me to get into 5e terms due to its beastlike nature and I want you to enjoy the experience.
[/quote]

Actually, got an idea (bear with me, still newish to 5e): 

If I changed my fighting style to Interception instead (when a creature you can see hits a target, other than you, within 5 feet of you with an attack, you can use your reaction to reduce the damage the target takes by 1d10 + your proficiency bonus (to a minimum of 0 damage). You must be wielding a shield or a simple or martial weapon to use this reaction) and be the tail hammer be more like a morningstar, which is a two-handed weapon so would take up both 'slots' and kept the shield as a reaction, would that work better?