Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Retro Circles Background 7 No Black
Source GDJ
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
I love the movie Pineapple Express, and I’m also liking this Pineapple right here.
Source Audee Mirza
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
Remixed from a JPG that was uploaded to Pixabay by Osckar
Source Firkin