[val@valcohen.com]

Change:

<select name=amount>
{if $products[product].min_amount le 1}
{assign var="start_quantity" value=1}
{else}
{assign var="start_quantity" value=$products[product].min_amount}
{/if}
{section name=quantity loop=$mq start=$start_quantity}
<option value="{%quantity.index%}" {if $smarty.get.quantity eq %quantity.index%}selected{/if}>{%quantity.index%}</option>
{/section}
</select>

to:

<input type="hidden" name="amount" value="1">

type="hidden" hides the form element, but still submits its value to the back-end.
value="1" tells the back-end you want a single item of the product.