Hi westernmom,
Congratulations on your new mattress 
I think you made a great choice and if you do end up deciding that you want a softer layer on top then you still have the option to exchange a layer.
You’ve probably seen this but there is more information about the different types of mattress protectors and some of the tradeoffs in post #89 here (and I just added some information about wool puddle pads or moisture pads). One of the waterproof membrane types would work well and are more waterproof and less costly than the wool/cotton protectors or puddle pads that use wool for water resistance (although a puddle pad can also work well for accidents) but the wool would be more more temperature regulating and uses more natural materials which for some people is worth the extra cost.
Phoenix