There is something called tenting that will allow you to go balls deep.. Different positions will help as well.. I love going balls deep but every now and then run into a girl where I can’t, it’s the price you pay having a big rod, I’ll pay that price, you may choose not to, especially if you think you will only ever have sex with this 1 girl for the rest of your life, in that case you may want to be cautious of length gains, and from your girth I bet you are satisfying her there too.
I guess you need to ask yourself, why you want a bigger dick, if it’s to satisfy her, talk to her about it, ask her honestly about her size desires. Personally I am doing PE for me, I have always been self conscious of my penis, and for some reason watching straight porn with dudes with huge dicks turns me on, and as far as I know I am totally straight, so I think having a bigger dick will be a big turn on for me, so it’s worth not being able to go balls deep.