A convenience method create an attributed string from a plain html string and apply a font of your choice. The method could be modified to support any fonts and styles.

AttribManipulator.swift

enum FontName: String {
    case timesNewRoman = "TimesNewRomanPSMT"
    case timesNewRomanItalic = "TimesNewRomanPS-ItalicMT"
    case timesNewRomanBold = "TimesNewRomanPS-BoldMT"
}

extension UIFont {
    
    class var sanFranciscoRegular: UIFont {
        if let font = UIFont.init(name: "SFUIText-Regular", size: 15) {
            return font
        }
        return UIFont.systemFont(ofSize: 15)
    }
    
    class var sanFranciscoItalic: UIFont {
        if let font = UIFont.init(name: "SFUIText-Italic", size: 15) {
            return font
        }
        return UIFont.italicSystemFont(ofSize: 15)
    }
    
    class var sanFranciscoBold: UIFont {
        if let font = UIFont.init(name: "SFUIText-Bold", size: 15) {
            return font
        }
        return UIFont.boldSystemFont(ofSize: 15)
    }
}

class AttribManipulator {

static func attributedStringFromHTML(html: String) -> NSAttributedString {
        guard let data = html.data(using: .utf8) else { return NSAttributedString() }
        do {
            let att = try NSAttributedString(data: data,
                                             options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType,
                                                       NSCharacterEncodingDocumentAttribute: String.Encoding.utf8.rawValue],
                                             documentAttributes: nil)
            let matt = NSMutableAttributedString.init(attributedString: att)
            att.enumerateAttributes(in: NSRange.init(location: 0, length: att.length),
                                    options: .longestEffectiveRangeNotRequired,
                                    using: { (list: [String : Any], range: NSRange, _) in
                
                if let font: UIFont = list[NSFontAttributeName] as? UIFont {
                    switch font.fontName {
                    case FontName.timesNewRoman.rawValue:
                        matt.addAttribute(NSFontAttributeName, value: UIFont.sanFranciscoRegular, range: range)
                    case FontName.timesNewRomanItalic.rawValue:
                        matt.addAttribute(NSFontAttributeName, value: UIFont.sanFranciscoItalic, range: range)
                    case FontName.timesNewRomanBold.rawValue:
                        matt.addAttribute(NSFontAttributeName, value: UIFont.sanFranciscoBold, range: range)
                    default:
                        matt.addAttribute(NSFontAttributeName,
                                          value: UIFont.init(name: font.fontName, size: 15.0)!,
                                          range: range)
                    }
                }
            })
            return matt
        } catch {
            return NSAttributedString()
        }
    }
}
}