I spent "whole" days away from my BF little bloke at around the same age. I got on with my day and my DH just called in for him to have his BF as needed. You could do the "whole day" spa and your hubby could just pop in with your LO so you could feed. I can't imagine that would be too difficult and it would give you both a chance to check in with each other.
Personally a whole day spa treatment would be torture for me. I just couldn't sit still that long.........I even put off having haircuts!