2SET,Stairway Baby Gate Mounting Kit, No-Drill Banister Adapter – Fits Posts 1.5" to 3.5" Wide, Universal Adapter for Pressure or Hardware-Mounted Gates

i have the exact same looking stairs as yours. i used this one side, worked really well https://www.amazon.com/dp/B0FFMVVV7G?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1 edit: now i am reading your banister is loose, i mean, that's it's own problem that will only get worse. so like other people said, probably fix that. even if you have a 1% chance of it failing on someone.. that fall can be debilitating.