I thought it was interesting what you said about INXJs and boundaries. Most of the INFJs I know were never initially that good with boundaries. However, with time and maturity and dealing with the results caused by a lack of clear lines in the sand, many of us end up improving on that. For me it is largely a function of:

1) Having a philosophy that my decision making is informed by (you've already got that).

2) Scripting myself in such a way that I have a line ready for what to say when I feel put on the spot. This allows me to decline graciously or to buy some time. When I have done this, it eliminated a lot of awkwardness in agonizing or in going back and cancelling out from the commitment I had made. The more I do that, the easier it gets even in new circumstances that were unforeseen and take me by surprise.