Wood for replacing trailer floor

I’ve working on replacing the flooring in a horse trailer that will mainly be used for moving cattle. From what I’ve read, oak (white oak specifically) would be the best kind of wood to use for the floor. My problem is, not a lot of places sell oak, I live in a pretty big city but from what I can find, only Home Depot sells oak boards (2x6 I believe, 8 feet long for about $140). The trailer is about 20 feet so the cost of the wood alone would be around $2500 to $3000. But I don’t even know if what Home Depot has is actually what I need.

I’ve also learned that yellow pine is an option. Cheaper, more available but obviously not as durable.

I guess my question is what does everyone use and recommend, and if oak is the way to go, are there specific companies I can buy online from? Also what sealer or other products do you like to use?