If you want to stick with a number and letter system, you could try Goldwell, otherwise consider brands such as Wella and L’Oréal.
Most of the main colour houses have their colour manuals available online to download or as an App which is very handy. Also, there’s the related brands. Kadus comes from the Wella stable so is a similar product.
I’d start by checking out your wholesalers and see what colour training they offer. They often have short intro colour courses to explain the basics of a particular colour house. They’re not usually very expensive and can prove invaluable when you’re trying out a new brand.
I think it’s important to read the colour manual when you swap brands because for instance, a lot of people untrained in Wella choose the /1 thinking they’re choosing a cool ash neutralising tone but it isn’t designed to neutralise only subdue tone so they don’t get the results they’re expecting and blame the product.
I have used a few different brands but you do need to use the matching brand developers to get the best from the product, so maybe factor that into your budget.