Crib mattresses.

So I received a crib with a mattress that was only used for 1 month because the mother didn’t like that the crib is a natural wood color and received a white crib with mattress through a program for single mothers. So according to my MIL’s neighbor who we are close with, she said it was only used for 1 month. The mattress would still be good to use? It was between this or my BIL’s crib and mattress which was more expensive but it’s 6 years old and used for two kids. I believe it’s a firm mattress and it has no rips, stains, etc. I’m very picky and have anxiety about safety. The crib will be used when my son is 6 months old since we will be using a bassinet in the beginning