Well i have a bit of a problem, my band is writing a song thats going great, I even get a nice long bass solo!

We jammed it through that part and it sounded sweet.
My only problem is that well my lines get a bit busy so its hard to keep track of WHAT i am doing, I mean I'm just keeping the groove and staying in the pocket and every time I play it my solo is different, there is no solid structure for every time I go in there and do it.
Now this wouldn't be a problem were it a live situation, but I still feel the song needs to be completed with a written out solo, that way when we tab it out on Guitar Pro and record it has a complete feel to it.
Any recommendations to help? The thing is whenever I go in specifically to write I lose creativity and just can't come up with stuff as easy that are just as good as my improvised stuff. I also don't want to keep the "studio" version too complex so I can actually remember it when i record, when I play it live I'll just do what i always do.