Wind can do a lot of damage to delicate plants & trees. You may need very hardy plants or put up some kind of windbreak, (incl. evergreens?). Cherries are nice, as are dwarf weeping willow,apples etc. Ferns are a nice, structured, lush evergreen, and easy to maintain, (tho they do need special acid soil & compost, all easily available). Ferns grow wild so there is nothing freer, but you'll need to check that you can take them legally. Made into fern "banks", they are very attractive.
One big drawback on trees in pots is that they quickly outgrow the pot, even large pots, and the only way to get them out is to break the pot, if allowed to grow large. Watering can also be a problem, as they can quickly become dry.
Assuming some wind protection, you could aslo try some roses. Nice in summer autumn, but generally nothing in winter.
Before you decide you could ask a horticulturalist to make some suggestions. The one I go to all the time is Kinsealy Garden Centre. They are very experienced and helpful with a wide range of stock. They can be a bit pricey, but you might get some useful tips. As for trees and plant, both Aldi and Lidl tend to stock a fair range. I saw some in there the other day. Go to the bigger stores, like Coolock. Hope this helps.