Let me be the first to say welcome. It's great to see new Who fans on here.:thumbsup
Now, about your request, you have several options out there. Some fairly simple (modding), to extremely difficult (machining from scratch). I'm no expert, & some others on here may chime in to fill in any blanks or correct me if I'm mistaken, but here's what I know.
If you're wanting a cheap, basic mod, There are several vids on YouTibe that show how to make the CO toy a little more accurate. Things like changing the button, getting rid of the spring-loaded mechanism, adding 'leather to the grip, filling in the hollow parts of the claws, & things like that. I've done this myself, & while time consuming, it usually yields good results if you take your time & don't rush. One bit of advice, watch SEVERAL of the tutorials before you decide which one you want to do. Some will be very clear, but the results will be a little lacking, while others will be hard to follow, but give you the best final product. This option will run you from $30-$50, depending on how involved you want to get.
The other option is to mod one of The Wand Co.'s Sonic Remotes. There are a few members here who have done this with fantastic results. I know of one that takes commissions & I personally own one of these. It's as close as you're going to get with what's out there, off the shelf right now. If you use the search feature here, you'll find some of the Work In Progress (WIP) threads on here that'll give you a good idea of how the mechanisms work. You may even decide to pick up one of the conversions when you see how nice they are. Here's a vid of the one that was done for me-
Eleventh Doctor's Sonic Remote Conversion - YouTube
Your last option is to machine one totally from scratch, which I can't do & would have no idea of telling you how to proceed. Again, the search option here is going to be your best friend with this. I'll warn you though. It'll take some time to go through everything, so make a good, strong pot of coffee & put your feet up.
Good luck with your project & keep us updated.