I want to create a proxy server after setting up IP limitations to use myself (multiple devices), and I want to set up multiple proxy servers in many kinds of devices.

For VPNs, OpenVPN is a single solution that works for almost all cases, but I find proxy servers to be more diversified.

I have various Ubuntu computers and VPS instances, and I find Squid to be predominant for normal computers.

However, I have two OpenWRT routers of which I want to set up a proxy, and the documentation said that it needs external storage for caching.

What is an adequate proxy server software to use without an external storage for routers with 16MB ROM and 128MB RAM such as the Mi Mini or Archer C7 v2-v4?