I work for a very large cosmetics company. Best way to get trained (and paid) is to get a job on a cosmetics counter and train through them. Though the will only train on their products, you can be trained to be a skin expert, therapist or a make up artist through these companies. Also, actual experience is a lot more valued than some of the courses that people pay a lot of money for.
pluses are 1. you get paid to train, 2. usually paid commission, 3. Often can train for management experience, 4. Dealing with public every day can build up loyal clients and a reputation 5. great benefits with cosmetics companies.
Minuses are that they are predominately selling roles, and retail hours can be tough (though also flexible which can be great if you are a parent)
Have a think about what interests you more, then go for it with relevant brands. I.e if you are all about skincare and being a therapist - Elemis, Clarins, lancome and Clinique would be the ones to contact
If you are more interested in make up artisit - Mac, benefit, etc.
You already have retail experience, so assuming you are good with people you will be great at it!
Honestly, as an employer - some of these courses are not worth the money that they charge.