Bed size for boy

[BTU]

Need buy a bed for my boy, he is now 4 years old.

Just wondering, what size should I buy, twin or full?
His bedroom is not big, twin size bed is perfect in the room. But, seems twin size bed to small for a boy.
Full size bed is good for him sleep, but no space for him move around.

Moms, please give some suggestion and advices.
What size of bed do you buy for your boys?
I think he will use the bed until 18, or until he move out later, hehe

Thanks

 

[Sean Mama]

现在买的床应该可以一直睡到离开家那天了，我是指18岁上大学去，那需要买什么尺寸的呢？要不然先买个床垫直接放在地方让他睡，过上几年再买。

 

[BTU]

现在买的床应该可以一直睡到离开家那天了，我是指18岁上大学去，那需要买什么尺寸的呢？要不然先买个床垫直接放在地方让他睡，过上几年再买。

Thanks Sean Mama.

Buy a good matress is not cheap, even for the twin size, still will cost $800 + tax.
And want buy other furniture, night table, dresser, together. If buy bed later, may hard to find matched one.