I will second git-spice. It does exactly what you want and, importantly, no more than that. There's no upsell to anything else; it's "just" a good tool that knows its purpose and boundaries.
replyHow does git-spice compare to git-town?
replyI haven't used git-town, but from a cursory look it appears to be a various collection of gitops improvements for day to day things, including some for stacking.
replygit-spice is specifically targeted to be useful for PR stacking and doesn't require you to do anything differently from normal git operations that you likely use already. It has a bunch of really nice flows and doesn't try to step outside the bounds of what is needed to easily stack PRs