Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Wild Oliva or Oliva Wilde? Darker than the others, sort of a medium dark pattern.
Source Badhon Ebrahim
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
A blue background wallpaper for websites. It has a seamless texture with vertical stripes. It looks quite nice not only when using as a tiled background on websites, but also on computer desktops.
Source V. Hartikainen
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
Retro Circles Background 8 No Black
Source GDJ
Background Wall, Art Abstract, Star Well & CC0 texture.
Source Ractapopulous
You know you love wood patterns, so here’s one more.
Source Richard Tabor
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
Sounds French. Some 3D square diagonals, that’s all you need to know.
Source Graphiste
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
Orange-red pattern for tiled backgrounds.
Source V. Hartikainen
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
A repeating background of beige paper with vintage look. Repeats to infinity, as usual.
Source V. Hartikainen