@heather: due to log of conditions there is no such easy way to do it. The best option will be to Set Default with sidebar. As there is more posts then pages. Then you can go to pages and edit it option to set as No Sidebar.
If you really want to do it from child theme then copy sidebar.php file to your child theme and then replace the following code:
// WooCommerce Shop Page excluding Cart and checkout
if ( class_exists( 'woocommerce' ) && is_woocommerce() ) {
with
if ( is_single() ) {
$layout = 'right-sidebar';
$sidebaroptions = 'right-sidebar';
}
// WooCommerce Shop Page excluding Cart and checkout
elseif ( class_exists( 'woocommerce' ) && is_woocommerce() ) {
Then copy the function fullframe_body_classes() to your child theme functions.php file and then edit the following code:
// WooCommerce Shop Page
if ( class_exists( 'woocommerce' ) && is_woocommerce() ) {
with
if ( is_single() ) {
$layout = 'right-sidebar';
}
// WooCommerce Shop Page
elseif ( class_exists( 'woocommerce' ) && is_woocommerce() ) {