New garden - help planning? Diagram included!!

[OrlandointheWilderness]

We've moved into a house built in 2018. The garden is laid to lawn, with a patio. We have two sliding doors to outside that form a corner, both windows are 6' in length. I have no idea where to try and put beds etc, we have a few trees to work around! I like cottage planting but I don't really know what I'm doing so I'm open to any suggestions!!!
Diagram below 😂

How big are the oak and horse chestnut trees? Are they already mature trees? Both will get absolutely enormous!

Trees are about 30'. They aren't that old. It's a rented house so the trees are here to stay 😂

Which way is North? Where the sunny and shady spots are in a garden will have an influence on what you can plant and where.

If it's rented are you allowed to put in flower beds?

Difficult to judge because lack of detail, where is the house? North point etc!

I would get some chunky wood off cuts and dig a curved trench and put the wood in upright in random heights make beds on either side. Big sweeping curves if you can. Include the tress in the beds then the rest can be lawn without bald patches around the trees.

Like this but it depends on scale.