We've also been looking at new bookshelves. Looked at Tylko - v nice and rather pricey, also Shelfstore (shelvingsystems.co.uk)
The Shelfstore would suit us if we had an odd size gap requiring a bespoke solution, but we have a plain 4.5m run to fill. Have narrowed down to 2 options:
1 - Ikea Billys
2 - random antique bookcases off ebay. There are some really great ones, and dirt cheap - noone seems to want big brown furniture. Bigger seem to be cheaper.