Yes Quinoa is a great alternative to couscous and is one of my favourite grains to serve with fish, meat and salad.
Robyn Russell in her book Gluten Free and Easy has a fantastic recipe for Quinoa couscous - you can find the book on www.glutenfreeandeasy.com

I am assuming you want to use psyllium as a gluten-free fibre to add to food. I am sure you know you wouldn't, for example, make a porridge with 100% psyllium but rather add a few teaspoons to the dish. You can use alternatives like rice flakes or millet to make porridge and then add your psyllium. Also you could try a sugar-free rice milk rather than cows milk and also add some flax seeds for extra fibre (they also contain healthy omega 3 essential fatty acids). Or why not add a teaspoon of FermPlus to your gluten-free porridge - it contains fibre, minerals, vitamins, essential fatty acids and lots of good bacteria. Add once you have finished cooking.

Another way you can replace rolled oats is with a gluten-free muesli. I make my own as most on the market are full of sugar. I buy puffed millet, puffed amaranth and add some pumpkin and sunflower seeds, a few raisins and some flax seeds, psyllium and some FermPlus. It tastes delicious.