i used progesterone. the baby apsirin thins your blood for good air circulation and blood flow to the uterine.
B12 and iron may help, too.
Some women get a thinner uterine lining on clomid, so I think just switching to femara/letrozole will help. Not really sure if there's anything you can take to thicken it, though, other than perhaps an estrogen supplement. Best of luck!