As has already been mentioned several time, K-1 is more expensive than CR1.
If you switch to the CR1, you will come closer to the cost of going through with K-1.
This early in the process, I think you should calculate the effort involved in terms of cost, time, processes and proceed as you think fit.
If a "stable union' is used to get benefits as a married couple, then I think you are walking too close to the line for comfort.
Search the forum, some people had engagement parties and were considered too married for K1. Stable union sounds even more than engage especially with what you plan to use it for.
My 2 cents .... no stable union