Book Symbols; Chapter Decorations, Ornaments, Fleurons; Separator Lines. Open the Sandbox / Playground link above in a new tab. Copy the symbols you want (one at a time) into that tab. Increase the font-size (see if 200 will work). Then, Alt+Print Screen to copy that window to your clipboard. Paste it into your graphics editor. Crop as needed. Increase the resolution to at least 300. I use 600. Save and then insert that picture into your Book Document.
Separator Lines: Many characters and combinations can be used to make separator lines. I find the following to be the most useful:
Asterisks: *****
Underscores: _____
—: —————
↔: ↔↔↔↔↔
∺: ∺∺∺∺∺
⋘⋙: ⋘⋙⋘⋙⋘⋙
╱╲: ╱╲╱╲╱╲╱
╳: ╳╳╳╳╳
▁: ▁▁▁▁▁
▂: ▂▂▂▂▂
▃: ▃▃▃▃▃
▄: ▄▄▄▄▄
▅: ▅▅▅▅▅
▆: ▆▆▆▆▆
▇: ▇▇▇▇▇
░: ░░░░░
▒: ▒▒▒▒▒
▓: ▓▓▓▓▓
▤: ▤▤▤▤▤
▩: ▩▩▩▩▩
◀▶: ◀▶◀▶◀▶
◎: ◎◎◎◎◎
☀: ☀☀☀☀☀
★: ★★★★★
☆: ☆☆☆☆☆
☸: ☸☸☸☸☸
♉: ♉♉♉♉♉
♒: ♒♒♒♒♒
⚛: ⚛⚛⚛⚛⚛
⛺: ⛺⛺⛺⛺⛺
✈: ✈✈✈✈✈
✤: ✤✤✤✤✤
✱: ✱✱✱✱✱
✲: ✲✲✲✲✲
✳: ✳✳✳✳✳
✴: ✴✴✴✴✴
✵: ✵✵✵✵✵
✶: ✶✶✶✶✶
✷: ✷✷✷✷✷
✸: ✸✸✸✸✸
✹: ✹✹✹✹✹
✺: ✺✺✺✺✺
✻: ✻✻✻✻✻
✼: ✼✼✼✼✼
✽: ✽✽✽✽✽
✾: ✾✾✾✾✾
✿: ✿✿✿✿✿
❀: ❀❀❀❀❀
❁: ❁❁❁❁❁
❂: ❂❂❂❂❂
❃: ❃❃❃❃❃
❄: ❄❄❄❄❄
❆: ❆❆❆❆❆
❇: ❇❇❇❇❇
❈: ❈❈❈❈❈
❉: ❉❉❉❉❉
❊: ❊❊❊❊❊
❋: ❋❋❋❋❋
❌: ❌❌❌❌❌
❎: ❎❎❎❎❎
❖: ❖❖❖❖❖
⟷: ⟷⟷⟷⟷⟷
⟺: ⟺⟺⟺⟺⟺
⦓⦔: ⦓⦔⦓⦔⦓⦔
⧍: ⧍⧍⧍⧍⧍
⧑: ⧑⧑⧑⧑⧑
⧒: ⧒⧒⧒⧒⧒
⧓: ⧓⧓⧓⧓⧓
⪓⪔: ⪓⪔⪓⪔⪓⪔
⿲: ⿲⿲⿲⿲⿲
⿻: ⿻⿻⿻⿻⿻
㞢: 㞢㞢㞢㞢㞢
ホ: ホホホホホ
🌸: 🌸🌸🌸🌸🌸
👄: 👄👄👄👄👄
💗: 💗💗💗💗💗
🔲: 🔲🔲🔲🔲🔲
🔳: 🔳🔳🔳🔳🔳
🔶: 🔶🔶🔶🔶🔶
🔷: 🔷🔷🔷🔷🔷
🔺: 🔺🔺🔺🔺🔺
😁: 😁😁😁😁😁