I hope it goes well for you. In terms of bands which you can get with the Ultra from Apple, you have three choices:
Ocean Band
Alpine Look
Trail Loop
Here are my thoughts as I own all three.
Alpine look is comfortable, but it's a nylon cloth and the Titanium buck at the end of the band if pulled far enough back can come in contact with the watch and possibly scratch it. If you do things which could get your band dirty, it may not be the best option.
Trail loop is a fancier version of the standard loop Apple sells for the other watches. It's a stretchy nylon and is admittedly sublimely comfortable, but again is't nylon and if you do things which could get messy or dirty, it may be hard to keep clean.
Ocean Band. To me, by far the neatest option. It's made of a high quality FKM Fluorolastimer, is super durable, won't stain, is comfy (though the other loop bands may be a bit more comfortable) and will last the longest of the three options you can choose.