You really shouldn't buy a special oil just got seasoning your cast iron and carbon steel. It's not necessary. Pick an oil with a high smoke point, a neutral taste, and plenty of easy availability. That's often peanut. Avocado is great if you're fancy.
Keep a squirt bottle of oil on hand and make sure you're using enough. Using soap to clean your pans will make maintaining your seasoning easier, as you use less effort to clean them. See this if you're skeptical: https://www.seriouseats.com/2014/11/the-truth-about-cast-iro...
I had friends dedicate years to flax seed oil. They're not happy about it, as they've got flaking to deal with. I also had friends disbelieve me that soap was okay, and they've mostly come around after hearing me swear by it for years.
Keep a squirt bottle of oil on hand and make sure you're using enough. Using soap to clean your pans will make maintaining your seasoning easier, as you use less effort to clean them. See this if you're skeptical: https://www.seriouseats.com/2014/11/the-truth-about-cast-iro...
I had friends dedicate years to flax seed oil. They're not happy about it, as they've got flaking to deal with. I also had friends disbelieve me that soap was okay, and they've mostly come around after hearing me swear by it for years.