Relaxed trousers get filed under "give up trying" in most wardrobes, the thing you reach for when you can't face a waistband that argues with you. I don't think that's fair, and I've got years of evidence on my side. A proper relaxed trouser is doing something quite specific with the cut, not just abandoning structure altogether, and on a frame like mine, where ordinary trousers stop a good inch above where they should, a well drafted relaxed leg can actually be the only pair in the shop that reaches my ankle bone without a single alteration. Inside leg 35 needed, several relaxed styles have given me 35 in the regular range. REGULAR RANGE. I checked the label twice because I didn't believe it.
They don't want much company above the waist. A boxy jumper or an oversized shirt on top of an already roomy leg turns the whole thing into something you could sleep in, and not in a good way, so a fitted top or something tucked is doing more work than you'd expect to keep the silhouette looking chosen rather than surrendered to. The difference between the ones that earn a second wear and the ones that end up folded at the bottom of a drawer is almost always the fabric weight and the waist construction. A heavy drape, a proper facing at the waistband rather than a flimsy fold of the same fabric, and a hem with enough weight to sit still when you walk, that's what keeps them looking like trousers rather than pyjama bottoms after three washes. The cheap version goes thin and clingy exactly where it shouldn't, usually across the seat, and no amount of ironing brings it back.
Where they genuinely fall short is anywhere you need a sharp line, an interview, a wedding where you want the outline to read as deliberate, or any situation involving a desk and other people's knees under a conference table, because the volume simply gets in the way. For a long train journey, a weekend away folded into a bag without creasing badly, or a day that starts at a desk and ends somewhere less formal, they are close to unbeatable, and they come out of a washing machine looking like you've done something clever rather than nothing at all. I'd start in a soft charcoal, dark enough to hide the inevitable crease from being sat in all day, before I went anywhere near cream.