1. Thank you for purchasing your new mattress with us. 感谢顾客惠顾的表达还有：
Thank you for shopping/purchasing with us.
Thank you for shopping/purchasing here.

2. Would you like us to deliver the mattress for you? 类似说询问需不需要寄送的话还有：
Would you like your mattress delivered?
Woulld you like to have your mattress delivered to your home?

3. We can have it to you at that time. 我们可以在那个时候寄给您。意思相近的表达：
We will deliver it at that time.
We'll have it to you at 12pm tomorrow.