I love writing and decided to put to rest some of my ghosts from the past by writing my life story so to speak.
I often write stories for my children but this is a little different.
A few friends have read the first few chapters and have commented I should have it published.
I have dismissed this , but wondered how hard it would be if I choose that route

Self-publishing is easy. Of course, you have to pay for it yourself. Getting a publisher to publish and promote a book is hard. It takes a big commitment on your part. You also have to be prepared to be disappointed. Many publishers won't even look at your work unless you're an established writer.

I knew someone that did self-publish a book on Breast cancer. She paid all up front costs.

You could consider "publishing on demand" which may be simpler.

How do I know if it is good enough to show to prospective publishing companies ?

Here is an example of a "print on demand" site from a search. "on demand publishing" is a lot different than publishing it on your own or having a publishing company do it.

You'll only know when you try and ask publishers.