Hi Wendy,
Post #4 here should help.
Since both of you are on the lighter side … you may prefer slightly softer foam in the comfort layer. Even your husband may prefer this although he may like a firmer layer than you underneath (much of the feeling of “firmness” of a mattress comes from what is under the comfort layer). While it is quite likely that a similar construction would suit both of you … there is always the option of a “side to side” split where each side is customized to the needs and preferences of each of you.
I have some fond memories of my waterbed days as well 
If they “fit” … they can be very comfortable.
Phoenix