First of all, be careful attacking w/ Yoshi, since he's not exactly the best rush-down character in Tekken. Adding the fact that Baek has punch parry, it might be a bit tricky if you are to use custom strings... (unless your opponent does not use Baek's punch parry, then just go ahead and outjab him) Just be careful not to make any mistakes during your attack, since a juggle from Baek ~ death.
Experienced Baek players can evade quite nicely and able to sneak a few attacks that give him frame advantages, such as u/f+3,4 and d/f+1. They can also add a few attacks that will give them relative advantages such as 3,"4", or d+3.
If he's the FLA cancel type of Baek, it's actually easier than you think. Baek's last attacks that ends 3 (left straight kick) can be side walked. An immediate side walk into d/f+2 outbeats his non-cancel left kick, as well as any of his attack option if he cancels it into FLA. Heck, if he likes to spam FLA cancel and NEVER ends it w/ 3, then go ahead and u/f+3 whenever u block his previous 3 hits (d+4,3,3,3~f or 3,4,4,3~f) or 2 hits (d/f+4,4,3~f). After eating a few juggles of yours, he will reconsider using the same strategy again.
NOW that if he decides to use the non-canceled 3 and you are still too lazy to sidewalk into d/f+2, you can always practice the stun-escape by tapping (or mashing) forward during the CH kick stun. During the stun-escaping, even if you press forward, you CAN block the incoming mid. (kind of like the DJ's CH b,f+2,1,"2" deal when you needs to press forward to "block" the third punch) After he realizes that the CH 3 tactics does not work, he will be forced to up his own game. Don't worry though, since Baek's a hard character in advanced play, he will have hell of a time to get better, haha.
Good luck, man.