Hey Seb - for 1 you should eliminate the idea that what tri distance you race.
Should have a bearing impact on your swim style or advice you will receive.
The thing that should differ with duration is your stroke rate.
Tone down your catch up, eliminate the over extension & no bilateral breathing.
If you look at the shots where your arm is fully extended.
Your head ‘bobs’ down under water and is fully submerged.
Breathing every 2nd stroke will help to keep your head higher.
As well to develop more a 1-2 rythym cause presently you don't have any.
And you should just switch breathing sides per length for ‘balance’ & versatility.
Your hand also pulls BESIDE your body under-water.
It should pull UNDER your body.
As for swim toys.
Small paddles so you have leverage and ease to maneuver your hands.
Only a band (no pull/buoy) to kill the gliding, contain your wacky kick and develop a hip thrust.
And shorten up your stroke out of survival - muahahaha