How to best purchase RAM upgrade?

It seems like nobody does this anymore. First I went to the Dell support website, entered my service tag and went to Parts and accessories. That all made sense and I thought this would be a simple 10 minute process to get the correct chips my laptop needed. There are so many different memory chips available, plus they seem to be changing all the time and not being a computer expert by any means, I was happy to see "Memory" listed as a category filter for my service tag search. Unfortunately all the joy left when it return three solid state drives and nothing to do with any memory chips. Can someone please tell me WHY would Dell not list them anywhere (spent another half hour looking) in Parts and accessories for your service tag???  How can we be sure they are the correct chips? I've joined and login and can search but under RAM memory there are too many different while very similar chips listed that may or may not fit the description under my service tag.

Next I tried a chat session thinking I could get someone to verify before purchase. It said "You are now being connected to an agent..." but a half hour went by and no agent typed one word. After an hour I started asking if they were having lunch and eventually someone came on. I had already moved on and started staining my back deck. Forget about Dell support, and the laptop will stay as it is - a new Inspiron 5559  that is slower than my 9 year old desktop. This used to work so easy in the past.