To recap: The Ectomorph is naturally very thin, has little shape & muscle, has quite a linear body & have seemingly longer limbs, aka your typical "skinny guy".
It's important to remember that a slim frame is much easier to dress than a large frame for two main reasons: 1. Clothes generally hang better on you and 2. designers design with you in mind, therefor high fashion and trendy garments seem to look extra good on you.
For your build, smaller retail stores like Hilton Weiner, Vertigo, Aca Joe, YDE, Country Road, Trenery, etc are better shopping options than the larger retailers like Edgars and Woolworths as they seem to have graded their sizes up (sizes going up to 3XL) to accommodate our overweight population in South Africa. (You might recall the results of a recent study putting SA right up there in spot nr 3 regarding countries with the most obese residents.)
Never wear over sized clothes in an effort to bulk up - this will have the opposite effect and place emphasis on your narrow frame.
When out shopping, look for "slim fit" as opposed to "regular fit" styles, especially in dress shirts (aka button shirts).
Avoid skinny jeans; unless the look you are going for is skater/ rocker. Straight leg or slim-fit, boot cut jeans are the better options. The taller you are, the more of a boot cut you may wear. Being short and wearing a wide boot cut will make you appear even shorter. If you want to wear jeans to work, for a business casual look, opt for darker shades in denims as they tend to look neater.
Avoid wearing dark colours from head to toe as this WILL have a slimming effect. Break up your outfit by wearing lighter coloured shirts like white, shades of light grey and shades of light blue. By wearing a lighter colour up top, your upper torso will appear larger and that will create the illusion of the ideal "Mesomorph" male body type.
Wear jackets with 1 or 2 buttons only. The more buttons you try and "cram" into a shorter space, the more of your length will be lost.
Also choose crew necks over V-necks for the same reasons as mentioned above.
Happy dressing or happy dressing your Ectomorph man! x