Just to clarify, this is the first time you have posted that you are in a D/s relationship. So that's probably why people had issues with some of the boundaries you and yoru husband have. Without the D/s context there will be different opinions.
As far as the 'get a dog' comment. I stick by it. I didn't say that YOU shouldn't submit to your husband or are his pet. What I said, if you stop and read it, is that what you are putting forward for this new person, SO FAR, reads more like an ad for a puppy. Someone to love your husband and be home for him when you aren't, to love you and be home for you when he's not. This post above is the FIRST TIME you have ever mentioned anything about wanting to be supportive of someone else's hopes and dreams.
I am glad that you recognize that the person you may want to be with may want things for themselves that have nothing to do with being available for you two when lonely and to accept and give love. As I tried to state, if what you want is a third, you will do better finding them if you are more careful on how you phrase things, be aware of how others will view your posts.
Your posts to date have read more one sided. More what we want from her and offering in return, love and a home. Which while great things, are not enough for a relationship. Only for a puppy. What if the new woman wants to move for work? Start taking classes full time and iS NOT able to be home for you two when you are lonely? What if she travels a lot? What if when she isn't traveling she doesn't want to be around others and needs more time to just herself? Many introverts do?
TL;DR 1) be aware of all the possibilities so you can be appropriately flexible and prepared.
2) Couples looking for a third are plentiful and often not saying anything new. If you want someone to take you seriously, be aware of what you are asking for and HOW you are asking it.
Believe it or not, it's not a prejudice. I personally don't want a ready made family of poly. However, for those that do, you have a daunting task ahead of you. See all those crashed bikes at the bottom of the stairs? The couples before you. See the people posting to you? Those same couples or those people that saw the couples crash their bikes. They are hoping by telling you "Hey this is how my bike crashed and was totalled!" You may not have such a bad wreck yourself.
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year