What type of hair straightening treatment to get?

I've had curly hair naturally my whole life. I'm white British, but both my parents are Irish and they both have that Irish curl pattern. People compliment me on my hair a lot, so I'm not saying this out of insecurity, but I want to straighten my hair.

I want to be able to do more intricate hairstyles that won't blend into my curls, I want to be able to dye my hair fun colours without worrying that my curls will drop out in an ugly way, and I want to reduce the amount of upkeep and money that goes into maintaining my hair. I'm just prefacing so I don't get the "don't straighten it, people would kill for your hair!!!" comments haha I don't want to be talked out of it, I just want advice.

Basically, my ideal hair type would be a medium to soft wave, around a 2A or 1C. Something that can still hold a curl if I were to try heatless curl methods or a curling iron, but on unstyled days it would only have a slight wave to it (photos attached). If I had to guess, my natural curl pattern is maybe a 2C or 3A (I've beaten the curls out of it quite a bit already lol), so not that far off. Is this achievable? Some of the things I'm reading say treated hair can still hold a curl, and others say they dropped out immediately if they even held at all.

I don't know how realistic it is to be able to choose my hair type in this way when getting a type of keratin treatment. I'm a little confused about the differences between all of them (I've seen Japanese Keratin, Brazilian Keratin, hair botox, etc all advertised as "smoothing" or "straightening" but never to what extent or really in any detail). What would be the best course of action for me achieving this hair type? Can keratin treatments only ever give you pin straight hair?

First 2 are what I want, last 2 are me :) I'm aware the reference pics might not be a "natural" wave like I'm describing, but even if I have to braid my hair overnight to get waves like that, I wouldn't mind.