My book is not searchable - Amazon saying I need a professional account?

I hope someone can help. Amazon is not helpful in this matter. I have a children's book listed as a product, however I noticed that it never comes up in searches, despite me putting in all the appropriate keywords. (here: https://www.amazon.co.uk/Mollys-First-Festival-Katherine-OShea/dp/1399954067?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A3MNUV8343Q0D6 )

After much debate and confirming my ASIN is searchable, I have been told that as it is a media product, I am required to provide a "subject keyword attribute to construct a keyword". However, this is apparently only available on the professional selling plan. At the moment, I don't even have the keyword tab available, just a tiny box in which to put "search terms" (and there is no way to separate these search terms with punctuation, so it seems very useless).

I just wanted to verify this as I don't think the professional selling plan is appropriate for me. I am one person with one product. I just want it to be found!

If anyone could please please help with this. I am a working mum and I just don't have time to go round in circles with Amazon support, and about ready to close the account down. I don't want to have to upgrade to paying £25 a month for something I don't need, or that still won't work.

Thanks

ASIN is 1399954067