Where to find a sleeper berth mattress?

I'm in a bit of hurry here as I'm typing this, and wasn't quite sure exactly where to stick this topic, so if one of the moderators feels like moving it to a "more appropriate" forum, by all means be my guest .

Anyway, I was just wondering if anybody knows where you can find a brand new, unused sleeper berth mattress? Be it in a truck stop shop, online, or in a common retail store, or anywhere else? Also, I'm not even sure what size to necessarily look for that would fit in the bed frame in the sleeper berth...? I think I've heard something like a Twin XL/Twin/or maybe even a Full?

I'm in school right now, and come October, will be starting my new career as a truck driver. While I do realize that of course, while I go out with my trainer, dragging a new mattress on his truck, along with my personal belongings - would be obviously ridiculous and out of the question. When I'm done training and get my own truck however, I'd prefer to have my own brand new mattress to sleep on every night, rather than just whatever old thing has been in there for who knows how long, used by however many drivers, who may have done God knows whatever they might have done on it.

So if you happen to know of any stores or sites or maybe even truck stops I suppose, that you can direct me towards. Thank you!

 

Oh believe me, I've already thought of that too. Especially after reading that one thread in the Werner forums about the trainer that s*** himself, or whatever exactly that was. LOL! I've been told that most car seat covers will easily fit a seat in a truck just as well, so I'm already planning on that. LOL! Not to say as though I'm quite a germaphobe. But do I take great pride in my personal hygiene and the fact that I am a completely clean, healthy, disease free, etc person? Yup you bet your *** I do!

 

As for the suggestions about checking with the company before I replace their mattress, I had already thought about that. If I have to replace it myself, I'll make sure to do so while I'm in town - at or by their home terminal, or at least at one of their terminals...maybe while I'm at orientation when I'm first assigned my truck. Then I can just hand them the old one and let them do what they will with it. I hadn't however thought to ask them to replace it for me. Don't know why, but the thought just didn't cross my mind that they might be willing to take care of it for me, upon request.
Thanks to all of you for the tips!