Hi lesibly,
Congratulations on your new mattresses 
As you know I think very highly of Tim and My Green Mattress.
I’m not so sure I would put them in the “too good to be true” category and there are certainly other memory foam mattresses in a similar price range with similar materials and similar return options but like some of the other online merchants in the memory foam list and the other members of this site they compete well with the best in the industry.
They are also not a member of the Better Business Bureau which affects and lowers their rating there (or the rating of any business that is not a member) but it is gradually moving up over time and they only have 2 unresolved complaints which may not even be resolvable or reasonable or they may not even be aware of. You can see some comments about the BBB in post #3 and #4 here along with points #1 and #5 in this post by a forum member and in post #4 here.
Your mattress forum search on Select Foam would have brought up every post in the forum that mentions them (and there are more than I have the time to sort through individually to choose a few) and you will find a wide range of experiences that include both glowing feedback and some of the challenges they have faced over time. A random example of customers that are very happy are in this thread and some comments about some of the customer service issues that they have had from time to time are in post #2 here.
Overall … outside of any individual experiences … it’s fair to say that they are a good quality/value choice that like other manufacturers offer a free return policy that can significantly lower the risk of an online purchase.
Hopefully others will also see your post and share any of their experiences with you as well.
Phoenix