Claire Shaefer’s pattern Vogue 7881 is a good pattern for tailored trousers and her explanation of how to make them couture is excellent. They are quite a wide leg, but this balances out the waist hip area if like me you don’t have a svelte figure
Use the size which fits around your widest part, so if you have a larger tummy area than hip, use the hip size for your widest part. You will probably need deeper back darts. Make sure your centre back is straight first and that your side seams are parallel, then take up the darts.
My tip would be to trace the pattern off if tissue fitting twice, so you’re not fitting just one side or an old sheet. I rarely make a toile, but trousers are the exception. Fit the back first. As we get older we tend not to be as erect, so will need to raise the waist band at the back. Take a strip of 1” wide elastic the circumference of your waist and stitch Velcro on the ends. Wearing the pattern, place this where you want the bottom of the waist band to be and mark with a pen, I find sharpies are the best, where the bottom of the elastic comes. It’s a good idea to extend the side and crotch seam allowance to 1” instead of 5/8” and the waist raise up 2”.
If the pattern has a fly front cut it off so you are just working with a seam, it’s easier to work without it. CF first, then side seams then darts/ease.You stick the extension back on after altering the centre seam, which will probably have a deeper curve, so the fly front extension will need to altered. Don’t try and slim down the legs too much between the hips and the knees. Moulding the trousers around your tummy will only emphasise it. It’s better to skim over and taper the trousers from mid thigh. Too much tapering will look like an inverted triangle, so you need to balance the slimness of the leg to your waist/hip area. This may result in the legs being wider than you want, but the trousers will look much better. Also if there are hip pockets, don’t cut them out for thetoile, cut the pattern so the front is complete, again it’s easier to fit than having to work with the gape the pocket produces. Once I’ve got the CF true, I then put a cheap zip in, to make it easier to keep taking the toile on and off.
It’s do-able on your own, but much easier with a buddy. Otherwise it’s just fitting a little at a time. My other tip is to baste the seams together, but with the seams on the outside, it’s much easier to repin. When the fit is correct, mark with a sharpie where the pins are and it should bleed through the fabric, resew this time with right sides together. I use a green sharpie to mark the final fitting lines so I know which are the right ones. My toiles can end up looking quite messy.