Change Default Store and URL with Store Name in Magento 1.9

Turn off store code urls in admin

admin > stores > configuration > General > Web > Add Store Code to Urls > No

run upgrade, static-content-deply and cache clean/flush commands

I had the same requirement and was able to solve it easily with just one plugin for Magento\Store\Model\Store::isUseStoreInUrl method.

public function afterIsUseStoreInUrl(\Magento\Store\Model\Store $subject, $resultIsUseInUrl)
{
    if ($subject->getCode() != $subject::ADMIN_CODE && $subject->isDefault())
    {
        return $resultIsUseInUrl && $this->scopeConfig->getValue('web/url/use_store_in_default');
    }
    else
    {
        return $resultIsUseInUrl;
    }
}

I registered the plugin in global di.xml instead of frontend because the first time this method is called area has not yet been set so the plugin would not get executed.