My initial plan is to bandsaw out the upper and lower curves, (ending up with a humpback bridge sort of shape), then bandsaw out the front/back curve. By doing it this way I should be able to sit the original on the hump and get a fairly accurate shape of the back curve
Yes, that's the best way - if you have a bandsaw. A couple of dobs of hot melt glue should hold it together when you are make the second pair of cuts. TBH you would be better off marking out the end flats, which will be at an angle to the front if the timber, and sawing them first, then chopping out the mortises (drilling and chiselling)
Then a case of roughing to near size with surforms, linishing belt sander etc and hand sanding.
Whatever you have to hand, really.
As anaside, just been looking at domino jointers and can only find Festool one. Don't any other manufacturers like Makita, DeWalt etc sell them? Can get biscuit jointers galore but not domino jointers.
Nope. Festool invented them and patented the idea and whilst there are some cheaper Chinese knock-offs around (on eBay), to date none of the mainstream manufacturers has bitten. Maybe it's because the market is a bit small, especially for something which for a one off could be done with a plunge router and some jigging.
Same thing applies to Mafell dowellers - the principle of multi-boring on 32mm centres (or multiples thereof) is long established, so in that instance there could be no patent, yet the only knock offs came from one or maybe two firms in China, and they are/were truly awful! (A bit like cheap biscuit jointers - but even more accuracy is required).
If you think about it, Steiner Lamello started making biscuit jointers in the early 70s(?) at eye-watering prices, it took Elu about 8 to 10 years to come up with a design which circumvented the Lamello patents (and even the DS140 wasn't cheap in 1981/82), and maybe a further 3 or 4 years for Bosch and Virutex to bring theirs onto the market. Now everyone and their dog makes a biscuit jointer - and some if the cheap ones are horrid... So perhaps give it a few more years?