Ill try and be helpful. I have the exact same type of body.
Your trap muscles make your shoulders slope more than average. So even if you find the right "size" for your chest the shoulders will be too aggressive. if you look carefully, there is a big height difference between your shoulder bone, and the shoulder of the suit. So aggressively padded suits with high armholes are not your friend. You'll run into this problem when you try on suits like RL Black Label, Boss, Z Zegna...etc.
You complain your arms are tight because your shoulders are dragging down the high armholes. If you shrug your shoulders upward in the mirror, the tightness will be lessened.
What you need is a very soft shoulder minimally padded suit. Try the classic neopolitan style tailoring with soft shoulders and minimal padding. I usually stick with Corneliani Leader model, most Canalis are also good, but what you are looking for is a very soft shoulder. And a suit for you has to be Canvased. A fused shoulder will not drape over your sloped shoulders as well and cause either side or top divots.