Uh, me and you are in the same boat, mate. I use only large tips to get a better seal, and in case of orange tips - they push the shells a little out. Get Shure olive silicone large tips -
https://www.sweetwater.com/store/detail/EASFX1-10L. I have them on all of my Westone iems. It's the same nozzle diameter, the same isolation level, and they are a little shorter. Trust me, those will be it for your comfort and the best fit. Here you can buy them in a pack of 5pairs for about $15 from sweetwater, though not sure where you can get it in UK, but google the model number.