No problem. You will get 30 days Visa Exempt when you enter Thailand and 90 days Visa Exempt when you return to Malaysia. No restrictions on how often you can enter Malaysia.
Ivan McAvinchey - Well, I never used to have a problem until six months ado. Same, I was told I can't return on the same day but I did overstay by 1 day as well. It's definitely a bugger if you can't come back the same day as the first reasonable hotel is 18 km further south from the border. No problem on my last border bounce and will tell you what's happen, as I have to go tomorrow again.
Back in time, you didn't need WP to get NON-B if you had a company. Then they changed. 5 years no need for WP if you invest, then it was 3 years and now, I don't know.