A noodle. I had to use one in late pregnancy with a few stones of baby bump pulling me down in the middle!
They're used a lot in children's lessons and don't overly float you/ change your angle.
I went to adult lessons at 16.
The first thing the instructor did was work on my kick, slow it down and get the technique right. For front crawl, I imagine that I'm just shuffling my feet (like tap dancing). That keeps my kick smaller and from the thigh not the knee.
Then we worked on breathing/ arms. I slice my hand into the water. As I cycle it out, I've breathed out ready and I breathe in to my arm pit. I could only do single sided for a long time then got the hang of alternating on the 3rd breath
I'm self-taught in breast stroke. The DCs were taught bend, star, snap for the legs. At "bend" as I pull my legs into a diamond, I put my soles together to keep it more symmetrical. I kick, then arm, kick then arm.
These days there's lots of youtube videos that are good for technique and instructions.
I'm so glad I learned to swim. I got from 25m to a mile in a year and I now swim open water.