Koss Porta Pro probably ticks all of the boxes for you. Drop has them for $38 right now here : Massdrop x Koss Porta Pro X Headphones | Open-Back Audiophile | Drop
If price isn’t too much of an issue have you tried OPEN over the ear headphones. They sound great and do not have that paper cup effect due to them being open. The only downside is that others can hear your music as well but I guess they could with on ear ones as well, just not as “open”. If you were willing to go that route the Senn HD-6XX from Drop is a great buy at $220 and many folks including myself love these cans. I suggest those since you like the Sennheiser brand enough to buy the PX100 more than once. I do not always endorse Drop.com and I am not affiliated with them but the two headphones I mention above they have great prices on and are very popular from their site.