This may not be the most sturdy option, but it is the only harness I have ever found to fit my oddly shaped chihuahua (barrel chest, little waist, thick neck, she was always popping legs out of harnesses). It is a step-in style, super easy to get on.

https://www.amazon.com/dp/B08CCH3QW7/ref=cm_sw_r_sm_apa_glt_fabc_48PMPVJ7QG048ZBNT61E?psc=1