As someone who does triple science, I'd personally say if you genuienly want to do this combo, go for it.
If you want to do one of the three main sciences in the future (at sixth form), as long as you do well enough in combined, I think you generally still have the door open (I'm talking generally, not for specific really hard to get into selective sixth forms). So you're not closing science specific doors really. As long as you get high enough it doesn't matter that much at GCSEs.
However you may not be able to do certain language courses at some sixth forms if you don't take it as a GCSE (as far as I understand it), which is why I recommend, if you're commited to it, taking the languages. Also you're doing further maths, that definitely covers STEM bases, in fact more than triple does imo
Basically, this combo closes off pretty much no doors to you, as far as I can tell. It's pretty extensive and varied. Bear in mind, that's 10 qualifications by my count. I personally take 9, you're in a better spot than lots with this combo
At the end of the day, this is just one person's opinion, please do not base your decision purely off of what I say. Consider about what you'll enjoy more etc, do some last minute research (I'm sure there have been others in similar positions) and talk to someone who knows you about it too I think
Best of luck with your decision