From the symptoms described (tripping the breaker) I'd say it's likely the heater element has failed. If the oven has other functions that also require the thermostat to work (such as top/bottom heating) you can use one of those and see if it reaches and maintains a temperature
I recently replaced the main heater element on my Bosch oven; the old one had failed visibly like most other heater elements I've replaced over the years, whereby there was an obvious split in the metal outer on one small part of the element. Your Bosch seems like mine - you may be able to get to see the element by removing a panel at the back of the oven compartment, but you'll need to take the whole oven out to perform a replacement. Found a pic of it with its door open:
Red arrow indicates the panel that hides the heater element: try removing it as see if the element is removable from inside the compartment (I think it doubtful due to the way the electrical connections are arranged) and if you can see or feel any damage to the element to confirm a problem. It might be obvious, with breaks or holes blown in it or even just subtly expanded like this:
If there are no obvious bolts to remove to detach the element from inside the compartment you'll be taking the back off the oven I expect - It is held into the kitchen cabinet by two screws near the top of the door opening. I arrowed these in blue on the picture above
The AC lead probably has a locking device preventing the plug from falling out; check for a sticker near where the lead connects for advice on how it works; a locking tab needs to be pressed or moved to remove it. Prepare a chair or strong helper person close by, as it's virtually guaranteed that there wont be enough AC lead to allow the oven to slide out and rest on the floor
New element from Bosch may be 30 to 40 quid (and with a long lead time, I found - took them 10 days to get round to shipping). Other spares places and copy parts likely available quicker and cheaper
