As for straight jeans or slim jeans ~ First of all, men's jeans are more casual, so you don't have to worry about how much thinner they will be than straight jeans ~ What matters is your preference and body structure. For intance ~ I am a girl, and I prefer boys to wear straight pants, which is pleasing to the eye regardless of whether they are fat or thin ~ Hehe, as for the jacket, you said that there is fat in the abdomen, so it is still loose and suitable for your color ~. You don't have to be black and thin, the basic color is a good choice, but you can't be black every day ~
For example, the lovely sunshine route is warm color ~ yellow pink.
Rational ~ blue-green or pinstriped shirt
All good choices, huh?
As for the figure you want to get better ~ then go to a gym and find a partner to keep exercising. If you can't do it yourself, you can't persist ~ If you are engaged in fashion, hehe, it is still helpful to have a strong body.