Call the store directly, they have a sum good products that might fit your needs. Typically what happens with flats or Matt's is you burnish, or end up polishing the surface. But they may have a paint that does not burnish when you wash.
"Duration" is good quality & washable ..BUT a flat or matte is still gonna show! Streaks wash marks etc. I'd go with an eggshell. Flat or mattes tend to NOT be washable, let alone really washable. Even a light colored Duration does not wash well in a flat or matte finish. I'm not aware of a really washable paint in any flat or matte finish. Sorry.
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