Teeth whitening strips wreck my gums. Any gentler alternatives that actually work?

I have tried Crest White Strips twice now and both times my gums ended up sore and irritated for days afterward. I want to brighten my teeth a couple shades but I am worried about damaging my enamel or causing more sensitivity. I know some people cut the strips in half so they only touch the front of the teeth and avoid the gum line entirely. Does that actually help or is it just wishful thinking. I have also heard about whitening pens or trays with lower peroxide concentrations but I am not sure which ones are worth the money. For anyone with sensitive teeth or gums, what actually worked for you without the pain. I just want results that don’t leave me regretting it every time I drink cold water for a week.