Self Spanking

My suggestions are:

Shower brush, nice wooden ones are available. The handle is long enough to administer a painful swat time after time.

Leather Belt, folded over so there are three strips of leather hitting your butt, not just two. Makes for a more effective strap.

Electric cord, looped into a two foot bundle and held with rubber bands at each end. Again an effective device for some self spanking.

Some sandals work well, but they have to be heavy but flexible.

It helps to use a stool to put a foot on. Spank the side that is in the air. The butt cheek is nicely presented and tight.

My experience taught me I HAD to find someone to deliver a spanking. When the pain hits, the ability to continue abates!