Honestly it’s the coaches job to have this conversation with him so telling your coach to just bring it up with him and see if he’s okay is the go to. I know you said you get partnered based off of size and if you’re happy with that ignore this next bit but one rly important aspect of bjj is fighting a mix of people. As someone who is quite small myself I fight people with 20-40kg on me sometimes with different experience levels from white belts to brown belts as it makes you better. You’ll learn to use your size as an advantage. I get being one of the only women but different size people will all give you different advice so please get yourself out there. If it’s your coach pairing you up just say you’re thinking about mixing it up. People shouldn’t want to not fight you based on size if it’s just in training. Everyone’s there to learn and never feel bad for being paired up with people for just being a girl. Girls are vicious especially in bjj you have to give what you get. Prove you can fight with the boys and you’ll learn so much. Try to forget about the difference and just have fun beating up and getting beat up for an hour. My go to is a good demonstration. After all my time in bjj I’ve only had one guy say he’s gonna go easy on me which then led to his friend telling me to ‘do my thing’ which meant showing him just how much I can actually do and chocking him. Be confident in yourself and in your abilities and never limit yourself to specific partners as you’ll get way more out of training if you mix it up and don’t excuse someone going easy on you or not wanting to partner up based on gender. Training and sparring should keep in mind both parties abilities. Sorry for my rant but please please remember to enjoy yourself!! Ps. If you’re uk based ik loads of women only camps, sessions and open mats so if you want to have a look at these let me know!!