Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Inspired by the B&O Play, I had to make this pattern.
Source Atle Mo
Zero CC tileable ground cracked, crackled, texture, made by me.
Source Sojan Janso
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
I love cream! 50x50px and lovely in all the good ways.
Source Thomas Myrman
Subtle scratches on a light gray background.
Source Andrey Ovcharov
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A new one called white wall, not by me this time.
Source Yuji Honzawa
From a drawing in 'Hundert Jahre in Wort und Bild', S. Stefan, 1899.
Source Firkin
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Horizontal and vertical lines on a light gray background.
Source Adam Anlauf
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Abstract Geometric Background 5
Source GDJ
Utilising a bird from s-light and some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Here's a new paper-like background for free use on personal and commercial projects (this applies to all background patterns here).
Source V. Hartikainen
I’m guessing this is related to the Sony Vaio? It’s a nice pattern no matter where it’s from.
Source Zigzain
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin