Downwards stretching never did anything for my girth, but maybe that's just me.
Besides SSJs (mix with Bends) and Compression Squeezes the
SRT size blaster is still underrated in its function as girth exercise imo (or maybe generally). It such a great exercise for girth, induces massive expansion! Also, as Longht suggested, edging with a cock ring (which is basically a clamping technique) is great for girth and it's a lazy ass mofo method to get expand significantly.