Until recently the game ran fairly smoothly and only crashed every two or three hours, but it's now doing it every twenty minutes or so. I installed the mod Unique Jewellery and Accessories yesterday and I think it's something to do with that, judging by my warnings file, but I'm not sure whether it's the mod causing the problem or the textures, if I'm right at all.

Here's the full warnings file:
Not able to find Foot part in BC_shoes_common_03.
Not able to find Foot part in BC_shoes_expensive_2.
Not able to find Foot part in BC_shoes_common_4.
Not able to find Foot part in BC_shoes_common_2.
Not able to find Foot part in BC_shoes_common_4.
Not able to find Foot part in BC_shoes_common_2.
Not able to find Foot part in BC_shoes_common_03.
Not able to find Foot part in BC_shoes_common_5.
Not able to find Foot part in BC_shoes_common_1.
Not able to find Foot part in BC_shoes_extrav_1_f.
Not able to find Foot part in BC_shoes_common_4.
Not able to find Foot part in BC_shoes_common_03.
Not able to find Foot part in BC_shoes_common_1.
Not able to find Foot part in BC_shoes_expensive_2.
Not able to find Foot part in BC_shoes_common_2.
Not able to find Foot part in BC_shoes_common_4.
Not able to find Foot part in BC_shoes_common_5.
Not able to find Foot part in BC_shoes_expensive_03.
Not able to find Foot part in BC_shoes_common_4.
Not able to find Foot part in BC_shoes_extrav_1_f.
Not able to find Foot part in BC_shoes_exquisite_1_f.
Not able to find Foot part in BC_shoes_expensive_03.
Not able to find Foot part in BC_shoes_expensive_03.
Not able to find Foot part in BC_shoes_common_4.
Not able to find Foot part in BC_shoes_common_1.
Not able to find Foot part in BC_shoes_extrav_1_f.
Not able to find Foot part in BC_shoes_extrav_2_f.
Not able to find Knee part in BC_extravagant_pants_02_Mk.
Not able to find Foot part in BC_shoes_common_5.

It goes on like that for some time. I also installed the Better Music System mod the other day, but I don't think that's anything to with it since I played for well over an hour with it activated without experiencing a crash.

Those are all harmless.
(they're just from mods that use clothing for Better Bodies.)

Try loading a much older save, preferably before the better music mod, and see if that crashes. If it does, load a similar save without any of the recent additions. That will help rule out those mods and save corruption.