There are many great places to buy pen, paper and stationary online. I have four places I go to. All of them are great, and they have fantastic customer service, I have never had a bad experience. Things have gone wrong with some of them, something I expect when I buy stuff from them time after time after time, but they have always done the right thing to fix the issue, without any hasitation.
GouletPens is my favourite place to shop everything related to pens. They have excellent customer support, their prices are competitive, and the experience from selecting the product until you unpack them are fantastic. Their blog is also fantastic; video reviews of pens, notebooks and inks.
JetPens is the place I go, if Goulet don’t have what I’m looking for. They are excellent, and they have more or less everything you are looking for.
Field Notes is my go to place for pocket sized notebooks. They are awesome, not too expensive and works great with more or less any pen.
Nock.co. This is the company Brad Dowdy of The Pen Addict started with Jeffrey Bruckwicki after a very successful Kickstarter. They make good looking, durable and functional pen & notebook holsters. My personal favourite is the Hightower.