Welcome to the forum. I am not sure of any sites, but people here will answers any questions you have.
I think the type of carrier depends on your cat. I have a soft carrier because Elliott freaks out when I put her in the hard carrier. She was biting and clawing at the bars so much she made herself bleed. Some cats may not be comfortable in a soft carrier, but some may not be comfortable in a hard carrier- you will just have to see what works best for your cat. I like the soft better because it is easier and more comfortable to carry them in.