If you were to ever discuss your new planting idea with10 landscape designers, you would probably get back 20 different plans with 50 different plants.
This is because they've all been trained in the same principles of design but have each learned to interpret the concepts differently.
The one thing they would all agree on though is the fact that every plant has its own specific environment where it thrives the best.
Place any plant in it's wrong environment and you are sure to not only compromise the integrity of your new design but probably eventually kill the plant.
I know a new landscape is on your mind the changes will be wonderful but you must not rush into this.
You really should spend some time in your existing garden first to try and observe what's happening there now so your future plantings will be happy in their new home.
You must learn;

• how much sun or shade will your planting beds get during the day
• what part of the day the sun is shining in the beds; is it morning or afternoon
• what type of soil you have, is it clay loam or sand
• how much room you have for the plants to spread out or grow naturally

When you have the answer to these questions, you will spend more time enjoying and less time working in your new oasis..
Like we talked about above plants thrive in their own environment.
Sun plants like full sun and shade plants like a little morning sun and afternoon shade.
You must do your homework and make sure the plants your choose fit your situation.
The soil you will be working with is very important to the future health of your garden and also to the amount of time you will spend caring for your plants.
Clay soil for example, holds moisture, drains slowly and has limited oxygen for the roots to absorb.
Install new plants in clay soil and in no time, the plant usually starts to take on a yellowish tinge to the leaf.
It's suffocating.
The reverse happens in sandy soil.
It holds very little water, causing the need for consistent water which you must supply Spread about 2 inches of compost on bothsituations and amend these soils and the plants will now work together with the soil to help you in you maintenance.
Since I do not know the actual size of your situation I will recommend certain plantings that will not get much bigger than 4 feet tall by 4 feet wide and will require very little maintenance as they grow.
They will not outgrow their space.
Plants for full to half day sun- afternoon sun, hotter sun;

• Spirea varieties - Bumaldi, Anthony Water, Little Princess, Gold Mound
• Caryopteris-Blue Mist Shrub
• Lilac- Meyer Palbin
• Barberry Crimson Pygmy
• Repanden Yew
• Boxwood Winter Gem
• Hoogendorn Holly
• Lavender
• Liriope
• Dwarf Burford Holly
• Calamagrastis Ornamental Grasses
• Pennesetum Ornamental Grasses
• Nandina Varieties
• Itea

Plants for half day sun to half day shade or morning sun, cooler sun

• Hydrangea varieties
• Repanden Yew
• Dwarf Burford Holly
• Variegated Liriope
• Hosta Varieties
• Acuba varieties
• Gumpo Azalea
• Heuchera Varieties
• Nandina Varieties

This is a good list to start from with many evergreen and flowering plants to choose from.
Continue to monitor water needs and airflow because smaller gardens may have limited airflow which can cause various leaf diseases if the moisture level stays high.
Good luck and good growing Peace Todd