Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
I asked Gjermund if he could make a pattern for us – result!
Source Gjermund Gustavsen
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
The image depicts an edo-era pattern called "same-komon" or "鮫小紋"which looks like a shark skin.The "same" in Japanese means shark in English.
Source Yamachem
Prismatic Abstract Background Design
Source GDJ
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel