What other coins to buy along with BTC?

I have been adding bitcoin to my portfolio each month (all in) for the past few minths. I have recently decided to allocate some of my monthly investment into other coins, and I was thinking something along the lines of: 60-70% into BTC, and maybe 20-30% into ETH and the rest into SOL. Am I on the right track or would you guys change anything? Let me know how to go about it please, thank you! I have started recently, and I'm just looking to grow my portfolio, but I still want the main focus to be Bitcoin.