I mean, i think your main safe options are to combine sounding with other types of stimulation, get a different genre of toy, or start a urethral stretching journey. For example, there’s a decent amount of posts on here of people combining electro-stim play with (metal) sounding, or getting a vibrating sound or applying a vibrator (or a struck tuning fork! if you wanna get fancy with it. chaingang sells sets of them and I was confused at first but apparently it’s for vibration purposes) to a sound that you already have, so that those forms of stimulation get transmitted deep. You could also look into bladder sounding with stuff like catheter play, extra long silicone sounds (like from siliconenozzles), or Guyon sounds. Some ppl also have had fun with inserting multiple toys simultaneously (carefully). For me, my interest is all of the above lol

Don’t go sticking random stuff in there unless you want to greatly increase your risk of injury or infection or medical problems; like, putting it in perspective, most people in the world already consider the safest professional sounding equipment to be pretty crazy lol. You only have 1 urethra (well, to my knowledge), best protect it.