MP3 and charger at the same time?

Are you looking for something like this.

https://www.amazon.co.uk/Belkin-Lightning-RockStar-Headphones-Certified/dp/B074WDWVX1?th=1

I would just make sure it's Apple approved, there are good and bad third party accessories, you ideally want the former!

I wonder if it's really just poor workmanship that's the issue or the fact in such an environment it's going to take an inevitable beating, all that plugging and unplugging is going to take it's toll, my lightning cable that's left connected to the iMac in a comfortable home setting hasn't lasted any longer than 12 months before I started getting syncing problems.

Maybe the solution is to try and cut down on the number of "mechanical" connections required, something like this.

https://www.amazon.co.uk/Bluetooth-Receiver-Streaming-Cancelling-Mpow-Black-Updated-Version/dp/B00KON1JIA?ref_=fsclp_pl_dp_1

Mind you, it still requires charging, for that it has to be plugged in, back to square one again (good reviews on Amazon though).

Maybe Belkin isn't so good after all, must admit didn't realise so many had given bad feedback on the Apple site, it's liked a little better on uk Amazon though.

Just wondering if some of the bad press has more to do with having to buy yet another dongle to do what they used to be able to straight from the box!

I don't know about "much better". A shade over 3 out 5 vs. 1 out of 5. A C vs. a solid F. Still the main negative complaint is it lasts a short period of time. I am guessing if you lay it down on a rock solid surface and don't move it or your device around it is okay. A bouncing car I am not so sure.

The OP needs to buy a new car every 5 years in order to keep up with Apple's changes. Isn't that the way we are supposed to do things? :-P

Maybe a third party solution

This one: Belkin 3.5 mm Audio + Charge Rockstar - Apple

or

https://www.google.com/search?q=iphone+headphone+and+charger+adapter

Which is the same product as in the Apple Store.

For your perusal: https://www.apple.com/shop/reviews/HLJV2ZM/A/belkin-35-mm-audio-charge-rockstar

Browsing the reviews many seemed to complain it just stopped working/flimsy after a short period. Shoddy construction. On the other hand there don't seem to be many alternatives out there.

It has much better reviews on Amazon. https://www.amazon.com/Belkin-Charge-Rockstar-Adapter-Charging/dp/B074WDWVX1

Interesting. Here's the US version

https://www.amazon.com/Mpow-Bluetooth-Receiver-Hands-Free-Assistant/dp/B075JBLGLB/ref=sr_1_3?keywords=bluetooth+receiver&qid=1553546638&s=gateway&sr=8-3