Smiler- I guess the way I look at it, is that it is Ratzon HaShem to do business with other Jews. Now, there are heterim when it comes to price and quality which, depending on the situation, it’s perfectly fine to rely on… but one cannot say they are fulfilling ratzon Hashem by not doing business with the Jew. They have their own cheshbonos on at what point to choose quality and price, which is perfectly in line with halacha, and it’s not our place to judge. Those who are machmir and willing to sacrifcie quality and price are almost certainly going lifnei mishuras hadin and fulfillinf ratzon HaShem.
Now, in your case, you aren’t sacrificing the Ratzon HaShem of doing business with Jews for gashmiyus, you are doing it for ruchniyus purposes. Which on the one hand sounds noble, but to me, it sounds a little misplace. Because you are sacrificing the Ratzon HaShem that is actually in the Torah, for a different potential Raton HaShem- not benefitting from a questionable mechira that almost all Rabbonim rely on. So, on the one hand, your chumra is a good one, in a vaccum… and it can seem like a better excuse to not buy from Jews that those who use gashmiyus… but how did you make that cheshbon that the ratzon Hashem of not relying on a sale is more important than the Ratzon Hashem of doing business with and supporting other Jews?