DIY Niu mirror, objective lens aperture 114mm, focal length 900mm, I want to see the moon, Jupiter and Saturn, etc. What size eyepiece should I choose?

When looking at the moon, a medium or low magnification of 10mm-20mm is fine; when looking at the planets, a slightly higher magnification is required, probably 7mm-10mm. The magnification of installing the 4mm eyepiece is too high, which requires high optics of the main mirror, operational proficiency, stability of the bracket and weather conditions. Moreover, low-end short focus eyepieces are tiring to use and the effect is not satisfactory.