Garmin trackers are super-duper - but why spend £150-£500 on a tracker when you can spend a fraction and have the same functions?
Look into the Xiaomi Redmi Watch 5 Lite and Mi Band 9. They have the same beautiful AMOLED screen as a Garmin, the same 18-21 day battery life, 150+ workouts, sleep tracking, continuous heart rate monitoring, alerts for exceeding safe heart rate limits, SpO2 monitoring,GPS so your route and speed of outdoor workouts are tracked, hundreds of watch faces to choose from, loads of different straps, the ability to control your audio while you train, and a water resistance to 50M, so you can swim with them on, etc.
The Watch 5 Lite can also make and receive calls and get all your notifications if you would like to replicate your phone on your wrist - which I don't. However, if you have cardiovascular issues, for example, and you were to collapse due to a heart irregularity during training, knowing you could just tap the crown 3 times to have a call made to your emergency contact is excellent.
My husband has the Redmi Watch 5 Lite and also the Mi Band 9 - which has the same functions and specs minus the phone calling as he likes the band's narrower dimensions as they allow him to wear a proper analogue watch to work and wear the band further up his wrist under his shirt. I use the Mi Band 9 as I've got tiny wrists and the Watch 5 Lite (being Apple Watch-sized) dwarfs me.
I think they are both about £35 on Amazon at the moment - cheap enough so that if you get bored of putting them on at night to track sleep or if you find that you only use the thing once/twice a week at the gym, you won't feel it was money wasted.
Or you could go uber-spangly and splash out on a Garmin!