@Alaskajt I encourage you to go the nostalgia way by choosing a double from years gone by. It's a fantastic choice. My first double is a VC 500NE which I love.
My third double was a Kriegoff 500NE which I just didn't care for so gave away to a good friend. Just a personal choice, nothing more.
My second, and favorite is my 1910 W.J. Jeffery 475 No 2 Jeffery. I've taken two of the Big 5 with it, Lion and Rhino (there I said it) and next year will take my second elephant and second buffalo with it- leaving only a leopard. I think it will be super cool to have taken all of them with this gun.
Some old doubles have cheek pieces some don't.
Some old doubles have a slight cast left or right, some don't. If you are a right hand shooter be sure the one you pick either has no cast or a right cast.
Be sure it has a length of pull that fits you, it doesn't need to be exact. If it's too far off changing the butt pad might get it where you want.
You'll have choices that are extractor guns and others that are ejectors. Ejectors will be faster to reload but only a second or two. My VC has ejectors, my Jeffery extractors. Both the lion and rhino I killed with a single shot so a moot point so far for me.
As far as caliber if you are not a reloader then keep to one that you can readily buy ammo for. Currently that's likely 450/400 3" (400 Jeffery), 470NE, 500NE.
Be sure the gun you choose has a proper weight, so for these three 10.5lbs, 11lbs, 11.5lbs (approx). Makes a huge difference for felt recoil.
Unless you plan on shooting a lot of Elephant you can drop the 500NE from your search if you want. If you think you might be recoil sensitive then go with the 400 Jeffery. Otherwise the 470NE might be your sweet spot.
As far as practicing, if you are a bird hunter with a single trigger you'll need a lot of practice going from the front trigger to the back for the second shot. Otherwise after shooting a few rounds to confirm zero(ish) most practice can be dry fire unless you just like shooting the double.
If you don't shoot a lot of open sight guns then you'll want a lot of practice here, but it doesn't have to be with the double, any open sight gun will suffice. For the first shot, as long as you don't flinch, you hold the gun steady, and you squeeze the trigger, it won't matter if it's a 22LR or a 500NE. Now the second shot...well...
Double gun hunting is a hoot. I really enjoy getting in really close and shooting off-hand as opposed to off sticks. I'm sure you'll enjoy it as well. Good luck on your search.
Three websites I watch for old doubles are:
https://www.gunsinternational.com/guns-for-sale-online/rifles/double-rifles-english.c286_p1_o6.cfm
http://www.champlinarms.com/Default.aspx?tabid=30&GunStyleID=3
(he might not actually have a gun he has listed- so be sure and call if interested)
https://stevebarnettfineguns.com/double-rifles