I did my last book with libre and got the proof back - it does not look bad at all. I showed it to a guy I know who was a printer for a publisher and who really does know a lot about the process. He was great with technical advice.
When self publishing it is important to try and follow the normal standards for a book. I literally scour the web for info on publishing and editing and so on. I also go for the 6x9 option as it also makes overall cost cheaper. However, that is not really UK standard.
No book will look good self published unless you also get an editor. The brain literally sees what you think you typed so you will never pick up your own mistakes.
Prior to anything going to the editor I also use www.grammarcheck.com and www.autocrit.com and ATD. They won't pick up everything or the sense of what you are saying but it gets some grammatical stuff ironed out.
I also do edit/find for mistakes like .. ,. ., etc. If you put the correction in it will find and change those for you in any editor.
Oh and just to depress us all who write. The cover is what sells the book and many people only apparently read a few pages of any book! (Got that from a publisher friend.)