my home directory is on a separate partition which still uses ext3. Is there a way to convert this partition into ext4 in a non-destructive way?
Yes, you can. This is explained very nicely in the ext4-wiki at kernel.org. Basically it all boils down to
with /dev/DEV replaced by the partition in question. Although this should be non-destructive, I'd still strongly suggest to back up your data before doing it.