Feed size question

I have a male spider, he was 109 grams last time I weighed him. Right now he is eating adult mice. He's a bit of a timid guy and the mice moving a lot kind of scares him a bit (he eat's, he just sort of hides until it slows down) most likely because of being in the new place and stuff. My question is how close to the size of an adult mouse is a rat pup? I was thinking something that didn't move as much might be better for him, plus theres the bonus that it can't hurt him like an adult mouse, right? Ive googled and from what I can see there is a big variance and stuff, but I wanted the pros opinions. Should I just get a rat pup (they'll show them to me so I can see the size and compare, but didnt want to waste their time if theres a big variance)

My snake is 137 grams and I feed him rat pups with no problem for about a month now! You can also get rat fuzzies if available to you. Ask for the smallest rat pup if thats all they got! Mine is a shy guy too so I stun the rat by shaking him in the container a couple of times then he just sits there in the tank and the snake grabs him. I do not like doing it this way but it works! He will refuse it if he thinks its too big!