Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
White circles connecting on a light gray background.
Source Mark Collins
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remix from a drawing in 'Ostatnie chwile powstania styczniowego', Zygmunt Sulima, 1887.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
There are many carbon patterns, but this one is tiny.
Source Designova
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Number five from the same submitter, makes my job easy.
Source Dima Shiper
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
The perfect pattern for all your blogs about type, or type-related matters.
Source Atle Mo
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
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin