Cat carriers for airlines (Manila)

Hi

I am Klara and I will be leaving Philipines next month with two cats. Has anyone knows what size and type of cat carrier would be accepted by KLM (going to Amsterdam) for transport of cats in the hold?

We bought already some large plastic cat boxes in Tiendesitas, but someone commentedthat they may not be big enough.

If you could let me know about any place where they sell correct type and size cat carriers in Manila, I woudl be grateful.

Thanks,

Klara