I like small phones too, but good options have disappeared and ok options are disappearing in Apple land.
You can get another SE1 but will probably lose support from your apps pretty soon if not already.
SE3 or 13 Mini (same processor) are the next smallest iPhones available. They're about 2 years old, but 6 years newer than the SE1, so comparatively they still have many more years of support ahead. The SE3 is still being sold by Apple, but 13 Mini you'll have to buy elsewhere, probably used. They have different form factors so if you can you should find a Mini to compare and see which feels better to you before buying. The 13 Mini has a better camera, more storage, an Ultra Wide Band chip, and uses Face ID instead of Touch ID if these matter to you.
Next smallest iPhone is over 6"--iPhone Pro, standard iPhone, or the rumored next SE(4)--so it's a pretty big jump.