Help with Past Perfect :)

Is this sentence ok?

I went to the gym for training this morning and bought two pairs of trousers on my way back home. As (Since) I didn't have any money in my wallet, I had withdrawn some money from a cash dispenser to buy the trousers.

I would say that the past tense is better to use in this context. I would write the last sentence:

I didn't have any money in my wallet, so I withdrew some money from a cash dispenser to buy the trousers.

Ok, thank you.

Why should you buy two pairs of trousers?

That wasn't my example. I was just interested whether it is ok.

>>Why should you buy two pairs of trousers?<<

One pair to surprise you in bed and the other to lambada you. ;)