Clothing for the unusual sized/shaped

I am new to cycling and originally bought relatively cheap clothing as I was (a) not 100% sure if I'd take to this cycling lark and (b) a bit of a fat git that looked and felt ridiculous in very tight clothing. Virtually all of my clothing is from Decathlon, so much so that I look like I'm sponsored by them. Now that I have cycled through the winter with gritted teeth and freezing toes and fingers, I am now ready to upgrade my clothing for some better fitting stuff. Shorts and tights are ok, its tops I have problems with. My problem is that I just can't seem to find stuff that fits me properly. I am 5'8, quite broad shouldered with a noticeably smaller stomach than I had this time last year (and I'm still working on it) and I find clothing either fits fine across my shoulders but is baggy on the chest and stomach and way too long in the arms and body, or it fits ok on the body, arms and stomach but is way too tight and restricting across the shoulders....

Anyone else have the same problem and got any suggestions of brands that might fit me better? I'm just after a couple of long sleeved tops and/or a softshell/windproof jacket.