Nash do one that fits your description perfectly it’s called the “Nash black ops Patrol pack”
I have one, you can fit plenty in it plus fit an extensive amount of outer pouches to the webbing if you so wish, it also has buckle fastening to attach the “Nash flat mat”
i haven’t had any issues with mine at all and had it for two seasons out in all sorts of conditions.
Obviously take notice of what others have said re quality as they obviously have personal experience using it and make your own mind up 😁