So I grabbed some t-shirting from the sash and set to this trouser project in the most cavalier fashion going (next to no measuring and pins weren't used at any point!).
They are made out of a grey t-shirting with dark grey and pink flowers on it. The waistband is elastic and they are loosely modelled on my home made tracksuit trousers.
There are no words for how comfortable they are! Currently they are a smidge too long (even by my standards) but as t-shirting has a nasty tendency to shrink after a few washes I'm leaving them for now. I can always cut the hem shorter in a few weeks.
They are going to be slob day trousers/pj bottoms for when I have guests round and don't want to be indecent when heading into the kitchen for my morning tea etc!