Hi Mar1nka. I'm a trained locksmith. The best fix is not necessarily the most expensive. I would recommend getting a good heavy lock and chain and leaving the chain/lock on site at work rether than carting it back and forth. That way you cna go for something heavy that affords lots of protection. Go to a trucking supply place or a fastener supplier and ask for several feet of "load binding chain" ( for sizing get the largest you can handle... 5/16" is pretty big, 3/8" is even better) . It will be a few bucks per foot. This stuff is hardened and will not be able to be cut with bolt cutters. It will be too heavy to haul around on the bike, but it will do a good job of securing the bike at work. Then get a padlock that has a shackle that just fits the chain and is protected or guarded so that you can't get boltcutters onto it either (example abus disklock) (Take the chain with you when you buy the lock to make sure it will fit) A Big box store will probably have the lock in the Master Lock version, or you may have to go to a locksmith. To protect the bike's paint you can use an old inner tube to slip over the chain.
Having said all that, a torch or power cutoff tool (eg a die grinder) will go through darn near anything out there, but you have protected against hand tools. Then by all means get a small lighter bike lock to take with you for when youy need to lock the bike elsewhere while you grab a coffee etc.