Crawling on hard wood floors

My lo is 4 months and desperately is trying to crawl! I usually have him in his nursery on the rug with a bunch of blankets on the ground for more cushion. But he slides a lot when trying to crawl because of the blankets and then gets frustrated that he’s not moving. I tried just having him on the rug but he got a little big of rug burn on his knee since his pants bunch up so I put a stop to that. Is it safe to have him try crawling on our hardwood? My MIL said I was INSANE for even thinking about putting him on there and threw a fit. He holds his head up perfectly and I would be right there with him. I didn’t really see any harm but I am a FTM so any input from experienced mom is appreciated.

UPDATE:

MIL wasn’t happy but I did it anyway! Little guy looked so happy! He was able to crawl a tiny bit!