You're not going to find a definitive guide because a lot of stuff is based on personal preference and overall combination of ingredients.
I'm just getting started on lotions and a resource that I would highly recommend is becoming a Patreon with Keeley at Soy and Shea (Create with Soy and Shea). She is absolutely amazing and I am in complete awe of how she finds the time to do all the things that she does, but then again, she is very well organized. She has a shop and is active on FB, IG, YT and her Patreon page. While she shares some recipes via YT, you get a heck of a lot more via Patreon and her private FB group. In addition to sharing all kinds of recipes, she gets in-depth on ingredients, provides general tips & tricks, resources, how to formulate, etc. She makes soap, candles, melts, bath & shower, face creams, hair care, hand & feet, moisturizers & balms, body sprays.