Just to add to the great advice you are already getting. Be aware koi can destroy your plants in your “bog” or what I would call planting beds built into the pond Or perhaps a passive bog. With put some planning, it can be done. Bogs tend to be around the edges of ponds and water systems in nature where they filter run off from land not actually in the water system proper itself.
In my first pond I built around 25 years ago, I added koi and had shallow shelves with plants in pots....they pretty much destroyed any plant that touched where they could reach. Long story short built another pond, as a plant filter for the pond with the koi in it, had around 7,000 gallons between the two ponds and the one pond was nothing but plants.
Then we moved 11 years ago and I built my second pond, which is 10,000 gallons. This pond has a lot of shallow planting beds made of pea gravel, as well as fine grain sand, a true bog filter ( bit undersized at the time) this time I planted the plants first and didn’t add koi until a year or so later. The koi were small too. Now 10 years later the planting beds are overflowing with plants, the koi ignore them for the most part, lilies growing in the pond, the koi ignore those as well. The only plant in my current pond that is in a pot is some Thalia and yellow flag iris everything else is planted bare root.
Point being with some planning and patience you can have koi and a natural eco pond as well. My current pond is loooaded with fish, koi, orfes, catfish, goldfish and 7 turtles. Filtered by nothing but plants, which I have used in both the ponds I kept with fish. I did upgrade my original bog this year in this pond, enlarging it to a centipede /snorkel/aqua blocks style bog, as the pind got a net strung up high over it to keep predators out, so without population control upgrading the filter system via a better wetland filter was a must.