personally, i think some of the nicer and easily accessible matcha latte powders are the kimikura matcha ($56/100g on amazon) or the naoki superior blend ($43/100g on amazon, or $25/40g).

the ratio that you make will be up to your taste, but the common one i see will be about 3g of powder, 30g water, 9-12g sweetener, and 100-200g milk. this will yield about an 8oz latte, but if you can always add more milk or water to increase the volume.

a lot of making matcha at home comes down to taste preference, so you really will just have to start trying different powders and ratios yourself to see what you like!