Where to check luggage in Kunming

I'm planning on travelling from Kunming to Guangzhou or to Beijing. I want to buy a hard sleeper bed for the journey. My big suitcase is 65CM in length and I think under 20kg. I am travelling throughout the holiday period and I'm worried there will be no room for my luggage. In addition to this suitcase I am also bringing a small backpack and a small light bag. Can I take these items on the train？ Is there an alternative cheap way to travelto Guangzhou or Beijing from Kunming Railway station ？