Here the "standard" initial biology book is the Curtis: https://www.amazon.com/Biology-Helena-Curtis/dp/087901394X

It's targeted to first year biology students, so it's light in the math part.

I'm currently reading through 'The Machinery of Life' by David Goodsell, and I'm really enjoying the intuitive explanations it has of the basic workings of cells. It's not a textbook by any means, but it provides a gentle intro to thinking about biological systems and seems like a great starting point.

Ooh thanks that's sounds great I'll have to give it a look!

I would recommend "Campbell Biology". This book is usually used for olympiad preparation. But, you may check it out first.

Campbell biology

That's the standard introductory book we use at university. (Introductory meaning that most of it will see you through to your bachelor degree.) I find it a very good book with clear explanations and well-designed graphics. A nearly equivalent option would be Purves.

Downsides: if you're only looking for a cursory introduction to a few themes, it's probably going to be too thick (weighs in at ~9 pounds) and too expensive (> $100).

Only if you buy the newest edition; an older edition should work fine for self-study since there's no classes to keep up with, and OP won't need the online component. I'm sure there's significantly cheaper copies of older editions where people just want to get that behemoth out of their bookcase.

True - and as the OP doesn't want to go into research, a few years out of date won't matter. (After all, it's not like there's been any major breakthrough in biology in the past ten years.)

I think the rule of thumb is that biology textbooks are 5 years out of date by the time they're published, so getting a slightly older edition is very practical.

Great thanks! I think my friend studying biochem may have this to lend. He didn't seem entirely sure that it was the best out there though, would you disagree?

It's the standard intro text and it's good enough.

I don't know that it stands head and shoulders above comparable texts, but it does what it sets out to do.

I believe it comes with a study guide which can be useful for self-study.

If the cost of a book is unappetizing, MIT's Intro to Biology on edx is great and free.