I am a mustachian feeler (ENFP), and I have also been known to shut down when I feel attacked. I think you need to frame it so that he doesn't feel like you think he is wrong, and are forcing this lifestyle on him. Also, I think if you can avoid talking about things spontaneously when he does something that frustrates you, and instead talk about things ahead of time, that might help. Try using "feeling" words relating to why you want to do something.
Example:
"I can't believe you just bought _______. Every time you do something like this you are delaying our early retirement" could very well lead to a shut down or a fight.
Try this over breakfast (or whenever you talk) instead, with no particular purchase up for discussion, "When we make large purchases without talking to each other, it really stresses me out. I feel my heart sink into my stomach. I want us to have all the things in life that will make us happy, but it would save me a lot of mental anguish if we could discuss the benefits of our large purchases before we make them." He might respond better to this. My guess is he loves you and doesn't want you to feel bad.
This leads me to another thought--have a discussion about everything that is a recurring expense (remember to use your feeling words--look some up or borrow phrases you have heard feelers use), and reach an agreement for each one. Then take that off the table for a while--you agree what the thermostat is set at, or how much you will eat out, or what you spend on the house, or spend on cars, and then you are DONE. No more talking about it, at least for a while. The compromises you make might not be the most Mustachian, but you can't win them all and keep the peace. Feel good knowing that you are doing great being married to a spender (that you love--remember that part) and being in the financial situation you are in.
Hope that helps.