Get good with thay trainer...Once you've learned how to land it, you're not ready for another airplane. I'm not saying that's what you think, just trying to make a point.
You need to master that trainer...Master it like you have your real Decathlon. Be able to land in the same spot (that you have picked) on every landing everytime. Be able to fly around the field inverted. Get good with your rudder (just like the real one) and get into some aerobatics. Practice loops, roll, spins, and all that other fun stuff.
Spend a good month (assuming you fly twice a week) if not more practicing with the trainer. Only when you've really got it figured out and mastered should you move on to the Decathlon.
I have heard a few stories about that GP Decathlon having some bad low speed characteristics, but I have never flown one myself. Make sure you've got the balance right and there are no warps in anything...It's not going to be the best 2nd airplane, but ought to work...
Do a search on this website for that airplane and you will get a lot of information. Then you can decide for yourself if you're ready.
Think of it as jumping in a real Extra 300 from your Decathlon...You wouldn't do it without some help, would you?
Now once you've gotten some good time in on the little Decathlon, you might find yourself cutting down on your hours in the real one...
Got a picture of your little one? Well the big one too now that I think about it...I'd love to see them.