Go to public library for advice, most libraries have pretty good idea what their books are like.
Best thing is to read THG for yourself (I did!). I think first volume of THG is okay, within tolerable for many 11yos. Most of the violence is only alluded to, not too graphic. But if they read the whole trilogy it gets more disturbing, a lot grimmer and more explicit. Bit like Harry Potter books in that the series matures with the readers. The real horror is in the society that endorses and glamourises the ritual humiliation. The books are quite political, too, towards the end. So I feel best left for older sensitivities to fully appreciate.
John Grisham does good thrillers, no sex or swearing but tense plots. I wonder about the early James Bond novels, too.
Bollywood Babes (one in a series of at least 3) are contemporary & not unduly about boys or romance.
Avoid Meg Cabot if you want to avoid romance.
Hitchhiker's Guide to the Galaxy, still modern enough methinks.
Darren Shan is very modern but gothic & violent. Ditto Steve Cole.