Boxus fits your description of what you want, its evergreen can be trimmed to shape and size and will not grow too big.
Heathers are also something you could consider?

also the sall leafed hebes have pretty flowers as well as evergreen foliage.

Also remember some plants like Heathers need Ericasous soil, so check plants soil needs. :o)))

Hello Legostan, wellcome to GOY. This isn't an answer to your question, but there is another GOYer on here, funnily enough called Balcony, you might want to look up some blogs. Hope this helps.

Hello again Legostan and welcome from me also. As you are new you may not have come across Goypeadia yet? Which has lots of ideas that you might like? Try pages like Container ideas, Annuals, Balconies, Evergreens even patio ideas? for lots of pics on how other members have tackled theirs. Just go to the bottom of the page and click on a large letter to take you to the list.
Pieris Japonica and Skimmia might also fit your needs?

I too have a balcony - luckily, mine's south facing, and which way yours faces is crucial - I get sun all year round out there, but if you have a north facing balcony, it will be in shade for 10 months of the year, most likely, and that makes a huge difference to what you can grow there. Do you have any idea which way it faces?

For labor saving tips, look for soil polymer, which can reduce the frequency of watering needed; or timed release fertilizers, which reduce the frequency of your feeding schedule. Otherwise, container plants always need more frequent watering and feeding than plants in the ground. Youmight also consider the fact that containers should have drainage holes, and should be watered enough each time so that water comes out the drainage holes, and don't like to sit in water in a saucer. Putting some thought into runoff management will probably save some acrimony with your downstairs neighbor.

Is soil polymer lighter TG? as that's a consideration too on some balconies.

I don't know what soil polymer is, Drc... but when I did my balcony on moving in, I used 45% vermiculite or perlite mixed with multi purpose compost in all the tubs to keep it lighter.

Soil polymer is a kind of plastic gel that can hold up to 40 times its own weight in water. It usually has no effect on how much the soil weighs per liter (density) outside of an increased difference between wet and dry conditions. agar is a more natural alternative, but it doesn't usually last more than a month or two in healthy potting compost. Bamboo has the right formula for lightening the soil, Legostan, but just remember that perlite has a slight drying effect, so is better for succulents and other plants that need fast drainage.

Thanks Bamboo and TB