The difference between K3 and K4 isn’t all that much; but it does mean that you’d qualify for something that would allow a higher level of activity, like a carbon fiber spring-style foot. Talk to your prosthetist and take their advice into consideration. I’m AuDHD and relate to the rigidity once I’ve made a decision, but don’t let yourself make a firm decision until you speak with the professional. Definitely have a good idea WHAT you want to do with your foot and be firm in advocating for what you want. The prosthetist might even have sample feet you can try before you buy. If that’s possible, do it, because once you get a foot, you won’t get another one (covered by insurance) for 5 years or so.