As someone that raised & bred discus for about 5 years in both bare bottom and high tech planted setups, Lennie's recommendation to go to simplydiscus is what I'd recommend too. Granted, I haven't been there in ages, but when I did go there daily, they were very helpful to those that were polite AND would take their advice. Knowledge of standard tropical fish care is a good starting point, but caring for discus can be a challenge. Adding the upkeep and maintenance of a well planted high tech setup can increase that significantly.
I cannot say anything beneficial about the places you purchased from. I will say when it comes to buying discus, discounts are not something I'd look for.
Unless you are buying from someone local, go for the sellers with decades of good reputation. Even then, they're quite an investment, so quarantine, quarantine, quarantine... with meds, not just observation.
Aquarium Co-op has done a few videos of the seller that I'd recommend too, but since they're not an official online recommendation of here, I'm not sure I can say their name. Search for discus on this company's YouTube page and that seller should be listed.
Good luck!