I would recommend using https://www.amazon.com/gp/aw/d/B074NCLZSW?psc=1&ref=ppx_pop_mob_b_asin_title latex hose instead of spring. It can collapse in on it's self unlike springs (in case you care) and you just add more loops/ pull them tighter to vary the strength.

Wow. Dangerous. That's why we use https://www.amazon.com/gp/aw/d/B074NCLZSW?psc=1&ref=ppx_pop_mob_b_asin_title instead of spring.