Advice of create my own crm or try and use others

I am currently in sales for a product which I sell to physical stores within my city. When I go to certain stores, maybe 2,3rd time is when they buy, I want to keep track of this. along with tracking the sales total and stuff like that so I don't have to use Excel and Google Docs to track my interactions.

I tried other crm's but they seem bulky and I don't want to pay, I only need small things not a whole fleet of features.

I have a pretty good idea of exactly what I need and my background is in tech so that i can build this, I just wanted to get some validation from people before i go ahead and start.

thoughts?