I don't think you were wrong for taking your friend instead of your husband. But I think you were wrong for excluding your husband from the process altogether. I'm sure his feelings were hurt that you didn't even tell him about it and just did it behind his back, when I'm sure he's very concerned about you and your health. It's like you were cutting him out of this very important thing.

I think the better thing to do would have been to have told him about it, rather than doing it behind his back, and then just explain to him that you wanted to have your friend with you instead. That would have at least given him a chance to discuss it with you and the two of you could have made a joint decision together, even though you would have the final say over who you wanted there. But at least he would have been part of the process and not felt like he was being excluded or replaced.

YTA