Yes, rolled oats is what you should use.
I make my own all the time, they usually turn out great but I tend to wing it so some batches are better then others.
3 cups rolled oats
3 tablespoons chia stirred into 9tb water and left to gel for 10 minutes (chia gel gives the muesli its crunch factor)
About 1/4 cup coconut oil
1 cup coconut flakes
Pinch of salt
1/4 cup each of brown sugar and maple syrup
1 cup nuts - I like pecans, almonds, or walnuts are also good, or mixed nuts - chop them up roughly
Handful of seeds - pumpkin, sunflower, pine nuts..
Mix it all up together and bake it for 30 minutes, stirring every 10 minutes, until golden brown. Your whole house will smell amazing.
After it's cooked add some chopped dried fruit like dates, cranberries, raisins, goji berries.
I've been known to have homemade muesli for dinner with ice cream and chocolate chips stirred in