Do you need a Sausage meal / premix to make sausages?

No.  Sausage meals / premixes can make it a lot easier to make flavoured sausages, but they are by no means required.  A premix is essentially a collection of ingredients, mixed together and packaged to make it easier to produce common sausage flavours.  If you use a premix all you need is water and meat to complete your sausage filling.  If you don’t then it is up to you how many ingredients you add to flavour your sausages.