Try this......
To make the TH sound press the tip of your tongue to the back of your upper front teeth, now gently exhale through your mouth.
To add the S sound let the tongue slip forward then drop it into position for the S motion.
It will not be a smooth continuous sound (that really is impossible even for native English speakers). Do it slowly at first then gradually increase the speed. The THS combination is always said a little slower than the rest of the word and is said and heard as a two part sound.
( I will never get ы sound correct)