I dont think the big issue here was the incompatile tankmates temul, because, you can keep species that dont REALLY need to be together for there entire lifespan, i think why they jumped on you (Ive been jumped on several times on this forum, they can be harsh, but they still my friends anyway lol, you'l get used to it) Is because your goldfish did need a bigger tank. What happens is, the fish cant grow anymore because it doesnt have ample space to do so BUT his/her organs continue to grow....once the organs get a certain size and start getting squished it eventually causes a painful death. I feel you could have kept the tank at 75 degrees and suited everyone perfectly 
actually im thinking of getting a Ryukin Goldfish for my 20 gallon when i reset it back up with 3-4African Dwarf Frogs and perhaps some Fancy Guppys such as the Blue and Yellow Cobra's and Tequila sunrises. Hope you stay here a long time and gain alot of knowledge, i remember i was just like you when i joined here, just hang in there and you'l learn to love this forum.
actually im thinking of getting a Ryukin Goldfish for my 20 gallon when i reset it back up with 3-4African Dwarf Frogs and perhaps some Fancy Guppys such as the Blue and Yellow Cobra's and Tequila sunrises. Hope you stay here a long time and gain alot of knowledge, i remember i was just like you when i joined here, just hang in there and you'l learn to love this forum.
