Yes, I think I can see what you mean. And I can guess it must be really disheartening, frustrating, dejecting (?) for you.
Just a few suggestions as it sounds like you've already talked to him about how his reaction makes you feel (although make sure he's absolutely clear on that and how you want him to be reacting):
Maybe focus more on the idea itself and putting it across?? Say something like "look I know (any obstacles) but this is what I want and (things that will make it work/important to you)". If it's about him, have a think about any obstacles he might throw up first and get straight in there with solutions/positives as soon as they come up.
Or perhaps just have more confidence in saying "This IS what I WANT".
Or maybe throw it over to him at times e.g. "Look well you have a think about something better, then we can discuss it a bit more". Open up some more discussion.
If the idea isn't going to effect him that much, go do it and give him the really positive feedback afterwards/let him see the results, let him see that you can make really good moves independently.
Sometimes have a couple of ideas, nothing wrong with being open minded, and say "look these are the options, what do you think, which do you think will work better.......or.....?". Then discuss.
This one, not quite so fond of, but if you have to use it to get the message across as to how his reaction makes you feel: React in the exactly same way if he's coming up with something you're not so sure about, and then in a bit let him know that what he might have felt is what he makes you feel when he....
And if he acts like one of your ideas was his idea then make sure you're reminding him whose idea it was.
But ultimately they're just suggestions, if you actually find that his overtones are invalidating in the relationship I'd say you really have to talk to him about this alongside the possible future of the relationship if this continues. You really shouldn't be in a relationship where you are feeling invalidated.
Best wishes
Alison