LIKE A FISH IN WATERike a Fish in Water

Titles are usually written in title case, unless there's a stylistic reason for doing otherwise.

I’ve practiced lots of sports throughout my life. Some of them were boring and dull, others exhausting and thrilling.

"throughout" is a more natural equivalent to "a lo largo de"

Despite how I’m interested in plenty of them, Sswimming’s always been my favourite.

Sometimes, "despite" needs something after it

You could also say

"Even though I'm interested..."

And, wWhat i's more, your skin is benefited by the warm water.

"what's more" is how I am used to seeing the phrase

"and" isn't necessary

It’s complete, funny and thrilling.

What are you waiting on to try it on?

The order was unusual.

I would expect to see something more like this (in terms of natural flow):

What are you waiting on? Try it!

I’ve practiced lots of sports through my life. Some of them were boring and dull, others exhausting and thrilling.

I just added a space after the full stop - may have been a typo :)

Despite I’mbeing interested in plentylots of them, Sswimming’s always been my favourite.

what you said was technically correct but this sounds more natural and how a native speaker would say it. Also, no need to capitalise the "swimming" here :)

Swimming’s a truly a complete sport, and it’s also really exciting by the way!

putting "truly" before the "a" sounds more natural to me although what you said is also correct. "By the way" tends to be used for something more unrelated to the topic; for example, it could be "swimming's truly a complete sport. By the way, I watched that swimming show the other day" It doesn't have to be completely related to the main topic of conversation but it's normally used to go in another direction. "Also" is used more for adding something to your point :)

As your muscles are growing, your breath is getting better and your heart is bombpumping, your body gets relaxed and you have a lot of fun.

"Bombing" wouldn't be used here - "bombing" refers more to someone exploding a bomb or occasionally used in slang as to either be drunk or to fail at something.

And, what i's more, your skin is benefited bys from the warm water.

"what is more" is correct but it sounds more natural with the contraction. "Is benefited by" is also correct but a native speaker is more likely to say that the skin itself benefits from the warm water as, in English, you'd often personify things to describe them (e.g., your skin benefits from the warm water).

A swimming suit and goggles are the only special objectsequipment required.

"Special" implies that something is uncommon. I changed it to "equipment" as it betters describes the swimming suit and goggles being things you need for swimming.

It’s complete, funny and thrilling.

I just added a space after the comma here :)

What are you waiting to try it onfor?

"to try it on" isn't typically used to describe an activity but more for trying on clothes/makeup etc.

I’ve practiced lots of sports throughout my life. Some of them were boring and dull, others exhausting and thrilling.

Despite that, I’m interested in plenty of them, Sand swimming’s always been my favourite.

As your muscles are growing, your breath is getting better and your heart is bombpumping, your body gets relaxed and you have a lot of fun.

A swimming suit and goggles are the only special objectsequipment required.

It’s complete, funny and thrilling.

Whaty are you waiting to try it onut?