Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Prismatic Groovy Concentric Background 5
Source GDJ
I took the liberty of using Dmitry’s pattern and made a version without perforation.
Source Atle Mo
New paper pattern with a slightly organic feel to it, using some thin threads.
Source Atle Mo
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
Floral patterns might not be the hottest thing right now, but you never know when you need it!
Source Lauren
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
This pattern comes in orange, and it looks as if it is "made of glass".
Source V. Hartikainen
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Used in small doses, this could be a nice subtle pattern. Used on a large surface, it’s dirty!
Source Paul Reulat
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A seamless pattern formed from a rectangular tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
I have no idea what J Boo means by this name, but hey – it’s hot.
Source j Boo
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Colour version of the original seamless pattern.
Source Firkin
A free green background pattern with a pattern of rhombuses on a seamless texture. Feel free to use it as a tiled background image on your web site.
Source V. Hartikainen
Remixed from a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin