Fountain Pens

Midori MD pads with one of their covers work well and aren't too expensive. Available in A5 and A6 if I recall. Otherwise as already mentioned I like the 90gsm Rhodia or Clairefontaine notebooks. The 80gsm Rhodia paper (found in a lot of their pads) always feels like the backside of the paper has less coating on it and not as enjoyable.

I've gotten good mileage out of Rhodia and Claire Fontaine, and my sibling swears by Tomoe River. Do not try Moleskine, I have gotten more feathering on those notebooks than on any paper I have ever used. I think they're designed for pencils, or something.

Fair disclosure, though, I usually just use cheap composition books, and find a pen/ink combo that looks good on whatever I happen to be using. I only use nice paper if I particularly need it for a given pen or ink, or if I am going to show someone else what I've written.

Hobonichi Techo is always good, but more oriented towards keeping a diary and a little expensive (though you get what you pay for).

I've really enjoyed my TūL notebooks. They don't seem very common in the FP forums, but they're easy to get a hold of in stores (in the US), come in many sizes, are expandable, and the paper quality works very well with all of my inks this far (it is not particularly quick to dry, but also not likely to feather).

My favorite notebook is the JetPens Kanso Noto. They have 160 sheets (320 pages) of Tomoe River paper with a 5mm dot grid. Tomoe River paper is a premium fountain pen friendly paper that should solve your feathering problems.

https://www.jetpens.com/JetPens-Tomoe-River-52-gsm-Kanso-Noto-Notebook-A5-Dot-Grid-Black/pd/29704

JetPens offers free shipping in the US for order of $35 or more. I don't know what options are available outside of the US.

The notebook is currently out of stock. I expect more to be back soon. Tomoe River paper was sold from one paper company to another. I think JetPens just cleared out their stock with paper from the original company and I anticipate they'll bring the notebook back soon with paper from the new company (Sanzen). In the past, the notebooks sold for $19.50, which is a great price for a premium paper notebook (seriously, I think only the Nanami Seven Seas notebooks have a better price per page for premium paper) . However, to keep the price low, the notebook doesn't have bells and whistles like an elastic closure or page marker ribbons.

Truthfully, I journal in a Mead spiral bound notebook. It works well with the inks I use (mostly Monteverde, Lamy, Diamine, and Sheaffer).

I use a Hobonichi techo planner and grid notebooks. I also use Midori grid notebooks. No feathering on both, not too glossy so my nib doesn't "skate" on top. I like Rhodia pads (some of the notebooks feather). Clairfontaine is lovely smooth paper but my pens usually "skate" on it and I can't control my handwriting on it, but YMMV.

Midori is lovely, especially for fancy inks - shimmer and sheen are more visible in my MD notebook than on Rhodia and Lechtturm papers that I’ve also tried. My favourite MD notebook is A5 grid additionally divided into 4 squares, works great for journalling and for the Goldlist method. No idea how this particular MD notebook is called, I buy it from Stilo e Stile.

@kalanggam As others have said, the Hobonichi's are great with fountain pens, or if it's more of a pure journal you're after the Luechtturm1917 Bullet Journal performs excellently.

I originally bought into the hype for Moleskine, but their paper seemed very low quality when I tried writing on it in person at the Moleskine shop in NYC.

Muji notebooks came very highly recommended for their price to performance ratio, and they're the real deal. I much prefer spiral bound notebooks that lay flat like this one, but they also offer a different kind of paper I haven't tried yet.