I will show you another way in another post.
Any slashed pocket like double welt, single welt or welt with flap pockets tend to sag if you actual use them to put something in it.
I always tell my husband to never use the outer pockets from his RTW suits except for a piece of paper because those pockets will sag.
But if you make your own suit jacket or coat you can prevent the sagging by using a tailors trick in sewing the pocket bag ( interior)
I learned this trick about 20 years ago during a tailoring course I took from a Dutch tailor, and I have no idea if this way of making a pocket is done by all tailors in Europe but I have never seen this technigue mentioned in tailoring books. So I thought this trick could be of use for all of you who are making a coat or jacket with horizontal slashed pockets .For angled pocket openings there are other ways to prevent sagging.
It does not take more than a few seconds, an iron and 2 inch/ 5 cm extra length of fabric or pocketing for the pocket bag ( Pocketing is a sturdy cotton or polyester rayon ( viscose) fabric used for pocket bags) but the difference in huge.
I made a sample double welt pocket and hung the fabric on a dress form to mimic a jacket or coat
here you can see the keys I used to put in the pocket
pocket sagging due to the weight of the keys,
The inside view of the bag with the keys inside
Pocket with keys inside, but due to the tailors trick there is no sagging.
I used pocketing plain green fabric (a sturdy cotton ) for the bag part but also used self fabric from the lower welt and a separate piece sewed at the upper welt seam allowance which is sewed at the pocketing part.
view of the welts are shown in beige color due to the beige colored fusible interfacing .
The trick is to make a pleat ( I used a 1 inch /2,5 cm deep fold) at the upper pocket bag part which is the side towards the jacket or coat, just below the first inch from the self fabric welt.
Inside view of pleated pocket bag with keys inside,
pocket bag stitched around included the pleat which is folded upwards.
view under pocket bag
Inside view from pocket opening,
Thanks to Kate in England a tailor in training mentioned in a comment that this is done in England too ( Saville Row way)