I'm not aware of a specific list of break DCs for objects in the core rulebooks. The DMG on page 238 does give some general descriptions of DCs, stating that "A DC 25 task is very hard for low-level characters to accomplish, but it becomes more reasonable after lOth level or so." The table goes up to 30, which is described as "nearly impossible." Obviously "very hard" is pretty subjective, and is offset by your character's ability score. For your character, you basically have a possible range of 24-33 in a strength check, so 25 would probably a light amount of effort. Anything below 24 would be essentially effortless.
A good point of reference may be to see what DCs are used in published modules. In the Curse of Strahd, for example, there are some crypts with 5ft x 3ft x 3inch stone slabs covering them. Removing or replacing these slabs is s DC 15 check (pg 85). There is a crypt with a large slab (pg. 93) which is 8ft x 6ft (depth is not listed, I would assume again around 3 inch). This one is a DC 20. Yet another tomb (also pg 93) is guarded by a portcullis (heavy metal gate) which is a DC 25 to lift. I cannot find any strength checks in the book with a DC higher than 25.
On page 33, the module says this about doors in the region:
"Doors. A wooden door can be forced open with a successful DC 10 Strength check, or DC 15 if the door is barred or reinforced in some other manner. Increase the DC by 5 if the door is made of stone, or by 10 if it is made of iron. Decrease the DC by 5 if the door is made of glass or amber, or if the door is weakened in some manner (such as by rot or corrosion). ... A typical padlock can be broken by smashing it with a bludgeoning or slashing weapon and succeeding on a DC 20 Strength check."