We also have a 1990 Triton 410 although it is now a bit different to the original. Like you intend, we have also dispatched the original upholstery in favour of a complete suit of cushions etc from an almost new but written off Bailey caravan which we had professionally altered to suit the Triton.
This Bailey upholstery is luxurious in comparison to the Eriba stuff and makes up into some very comfortable beds. So the best of luck with your new baby and I hope you achieve your desired effect, these things can take time but are well worth the effort.

Cheers, John & Wendy